Industrial and Engineering Chemistry : analytical edition, Vol. 2, No. 4

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Analytical

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4 A N A L Y T IC A L EDITION Vol. 2, N o. 4

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25 x 150 .l a 480 57.60

25 X 2 0 0 - u 360 54.00

25 x 250 .10 300 60.00

25 x 300 _•15 100 50.00

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Vol. 2, No. 4 A N A L Y T IC A L EDITION

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October 15, 1930 IN D U STRIA L A N D ENGINEERING CHEM ISTRY 7

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8 A N A L Y T IC A L EDITION Vol. 2, No. 4

TW O NEW S H A K IN G APPARATUS

8914

SHAKING APPARATUS, Ross-Kershaw. D esigned to im part to the con ten ts o f sixteen P yrex E rlen- m eyer flasks, 250 m l ca p a city, a circular agitation sim ulating th at n orm ally given in h and shaking.

C onsisting o f a square p la te o f B akelite, w ith clam ps fo r the flasks and m echanism fo r im parting the shaking m otion , m ou n ted on angle iron base w ith m otor.

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A nalytical Edition

Published by the American CheiniealSoeiety

Volume 2 OCTOBER 15, 1930 Number 4

Alum ina in a N e w Form as a Laboratory Desiccant 1

J. Bryte Barnitt, Ralph B. Derr, and Edward W . Scripture, Jr.

Al u m in u m Re s e a r c h La b o r a t o r ie s, Al u m in u m Co m p a n yo p Am e r ic a, Ne w Ke n s in g t o n, Pa.

T

HE absorptive prop

erty of partially de

h y d r a te d aluminum trihydrate has been known for many years, and in the many investigations (1 to 6) under

taken to determine the value and efficiency of laboratory d e s ic c a n t s , a lu m in a has usually been employed for comparison. A lth o u g h it

is recognized that the vapor pressure of alumina is very low, it has not been employed extensively as a desiccant because heretofore it has not been available in a form in which air or gases could diffuse readily throughout its mass.

Recently, by a special process, it has been found that pure aluminum trihydrate can be produced in the form of hard crystalline lumps which can be sized and gradecj varying from a powder to pieces approximately 2 inches in diameter.

This form of alumina, when suitably treated, acquires marked absorptive properties and when graded into sizes varying between 4 and 20 mesh permits the circulation of air or gases throughout its mass so that they may be rapidly and com

pletely dehydrated. Experimental work has shown that this new form of alumina, which is known as “ activated alumina,” compares favorably in desiccating properties with phosphorus pentoxide and other commercial desiccants with

out having their disadvantages.

Drying of Air by Passage through Various Desiccants

Although determinations of vapor pressure may not be considered entirely satisfactory for evaluating reagents so varied in nature as the common desiccants, it will be of interest to know the comparative efficiency of alumina and other desiccants by a method analogous to the dynamic vapor-pressure procedure. For this comparison, alumina, phosphorus pentoxide, sulfuric acid (96 per cent c. p.), calcium chloride, and barium-magnesium perchlorate were employed in a train through which air of high humidity was drawn under comparable conditions.

Approximately equivalent volumes of each desiccant were placed in U-tubes of like dimensions. In the tubes containing sulfuric acid and phosphorus pentoxide, glass pearls were added to secure exposed surfaces comparable with those of the other desiccants which, being of a crystalline nature,

* R eceived M a y 28, 1930.

A pure a lu m in u m trihydrate has been produced which, by suitable treatm ent, acquires m arked ab

sorptive properties and permits the circulation of air so th at it can be rapidly dehydrated. In the dehy

drated form this “ activated alum ina” can be used as a laboratory desiccant. The efficiency of this alum ina has been compared by various m ethods with other com m ercial desiccants, with very favorable results;

moreover it does not have the disadvantages of the other m aterials.

were graded through 8- and on 14-mesh screens. These U-tubes were connected in a train in the various orders indicated and air saturated with moisture w as d ra w n through at the rate of 3 liters p er h o u r . The inside di

ameter of the U-tubes was 1 cm. and the length of column was approximately 12 cm., so that at the above flow rate a fairly rapid linear flow was obtained. The experiments were performed at room temperature, which was constant for each test but varied from 22° to 30° C. in the different tests. Thus the total quantity of water absorbed was not exactly the same in each case, although the same amount of air was drawn through the train. In each test an additional tube con

taining phosphorus pentoxide was placed at the exit end of the series to prevent back diffusion and to serve as a check on the completeness of the removal of moisture. In no instance did this safety tube gain in weight. Thus it may be concluded that no moisture passed completely through the train in any case and that there was no diffusion from the exit end.

In Table I the position of the desiccant in the train is indicated for each test, and the gain in weight together with the percentage of water absorbed, based on the total quantity passed, is indicated for each tube.

In the first test alumina absorbed 99.9 per cent of the moisture passed through; calcium chloride actually lost water to the dry air; sulfuric acid did not gain or lose;

and the phosphorus pentoxide absorbed the 0.1 per. cent moisture passed by the alumina together with the 0.1 per cent moisture removed from the calcium chloride. In the second test the position o f phosphorus pentoxide and alumina in the series was reversed, and in this instance the former absorbed 97.8 per cent of the total moisture;

both the calcium chloride and concentrated sulfuric acid absorbed small amounts, while alumina absorbed the residual moisture amounting to 1.8 per cent of the total. In the three subsequent tests sulfuric acid, calcium chloride, and barium-magnesium perchlorate occupied the first position in the series, and in each instance less than 95.2 per cent of the total water passed was absorbed in the first tube. Alu

mina preceding the phosphorus pentoxide tube absorbed, within experimental error, the residual moisture. The

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356 A N A L Y T IC A L EDITION Vol. 2, No. 4 performance of barium-magnesium perchlorate was checked

by several runs. When this material was preceded by either alumina or phosphorus pcntoxide, it gave up to the dry air part of the moisture absorbed in the two previous runs.

Since the efficiency of absorption of water from a current of gas involves the rate of absorption as well as the vapor pressure of the absorbent, it is apparent in cases such as these, where equilibrium may not have been established, that the amount of residual moisture in the gas will be affected by the rate of flow and by the contact obtained between the gas and the absorbent. These factors account for the fact that phosphorus pentoxide did not give complete drying under the conditions employed, and the results illustrate the difficulty of obtaining high efficiency where satisfactory distribution is not readily secured.

F ig u re 1— D e h y d r a t io n o f C o p p e r S u lfa t e P e n t a h y d r a t e o v e r A c t i

v a ted A lu m in a , S u lfu r ic A c id , C a lc iu m C h lo r id e , a n d B a r iu m M a g n e s iu m P e r c h lo r a te

Dehydration of Copper Sulfate Pentahydrate over Various Deslccants

A more satisfactory method of determining the efficiency of a laboratory desiccant is that of employing the exact conditions obtained in a desiccator. Hydrated manganous nitrate (MnSCh. 6HjO) has been employed b y Smith (5) for the determination of the efficiency of perchlorates;

Marden and Elliott (4) have employed hydrated copper sulfate (CuS04. 5II20 ). In the present writers’ opinion the latter material is the more suitable for this purpose because of the low' melting point and transition temperature of the former. Therefore, in the following experiments equal quantities of copper sulfate crystals were placed in similar weighing bottles over the various drying agents in Scheibler desiccator jars. The samples were weighed periodically until practically constant weight was reached. Then the copper sulfate was completely dehydrated by heating at 175° C. to determine the residual combined wTater. In a second test the copper sulfate crystals were ground to a greater degree of fineness and the determinations of the previous test repeated with the substitution of barium

magnesium perchlorate for phosphorus pentoxide. The results of these experiments are summarized in Table II, and Figures 1 and 2.

The dehydration follows a similar course in each instance.

For a short period at the beginning very little moisture is lost to the desiccant and no visible change occurs. A period of rapid dehydration follows; light spots appear on the . copper sulfate, and these gradually increase in size and number until the surface is completely covered wdth pale blue monohydrate. At this point the material reaches a nearly constant weight and the coating decreases the speed of diffusion to a negligible rate.

T a b le I — D r y in g o f A ir b y P a ssa ge t h r o u g h U -T u b c s C o n t a in in g A lu m in a , P h o s p h o r u s P e n to x id e , S u lfu r ic A c id , C a lc iu m

C h lo r id e , a n d B a r lu m -M a g n e s iu m P e r c h lo r a te

Position in series 1 2 3 4

1st Test:

D rying agent AlaOa CaCla HaSCU PaO*

Gain in weight, gram + 0 .0778 - 0 .0 0 0 1 * 0 .0 0 0 0 + 0 .0 0 0 2 HaO absorbed o f total, per

cent 9 9 .9 - 0 . 1 0 .0 0 .2

2nd Test:

D rying agent Gain in weight, gram HaO absorbed o f total, per

cent

PaOi CaClj HjSOi AlaOa

+ 0 .0 7 6 4 + 0 .0 0 0 1 + 0 .0 0 0 2 + 0 .0 0 1 4

9 7 .8 0 .1 0 .3 1 .8

3rd Test:

D rying agent Gain in weight, gram HaO absorbed of total, per

cent

HaSO< AlaOa C aC l. PaO*

+ 0 .0 8 5 3 + 0 .0 0 4 2 + 0 .0 0 0 1 * 0 .0 0 0 0

9 5 .2 4 .7 0 .1 0 .0

4 th Test:

D rying agent Gain in weight, gram HaO absorbed of total, per

cent

CaCli HaSOi AliOi PaO»

+ 0 .0 6 9 8 + 0.0002 + 0.0034 * 0 .0 0 0 0

9 5 .1 0 .3 4 .6 0 .0

5th Test:

D rying agent

Gain in weight, gram

B a-M g perchlo

rate + 0 .0 9 3 1

PaOs + 0 .0 0 5 4

AlaOa + 0 .0 0 4 2 HaO absorbed of total, per

cent 9 0 .2 5 .6 4 .2

6th Test:

D rying agent

Gain in weight, gram HaO absorbed o f total, per

cent

AlaOa

+ 0 .1 0 6 1 B a -M g perchlo

rate

- 0 .0 0 1 7 PaOs + 0 .0 0 3 2

9 9 .0 - 1 . 6 2 .6

7th Test:

Drying agent

Gain in weight, gram

PaO 5

+ 0 .1 1 1 0 B a-M g perchlo

rate - 0 .0 0 0 9

AlaO, + 0 .0 0 7 0 HjO absorbed o f total, per

cent 9 4 .8 - 0 . 8 6 .0

We ig h to p Dr y in g Ag e n t s Em p l o y e d

Grams Alum ina... 10.52 Phosphorus pentoxide... 2 .5 0 Sulfuric a cid ... 7 .2 4 Calcium ch loride... 10.27 Barium-magnesium perchlorate... 18.53

T a b le I I — D e h y d r a t io n o f C o p p e r S u lfa t e P e n t a h y d r a t e o v e r V a rio u s D esicca n ts®

Fir s t Te s t Se c o n d Te s t

Tim e

AIjOj PaO» HaSO< CaCla AlaOa HaSO» CaCla B a-M g ELAPSED

170 35 430 160 225 250 225 perchlorate

grams grams grams grams grams grams grams 450 grams

Days % % % % % % % %

2 0 .3 0 .2 0 .3 0 .0 1 .1 0 .7 0 .6 0 .5

4 0 .3 0 .4 5 .0 0 .0 1 .3 5 .9 0 .6 3 .9

7 15.6 2 .3 2 2 .2 0 .2 2 1.6 2 9 .6 13.1 1 2.3

9 3 0.2 6 .5 3 4.0 2 .4 4 6 .3 5 3 .5 4 0 .0 2 4 .0

11 4 0.7 15.0 4 1 .0 15.5 55.1 5 4.7 5 2 .5 3 4.2

14 42.1 3 0 .2 4 1 .7 3 6.5 5 5 .5 5 5 .0 53.1 4 0 .0

16 4 2 .3 3 7.6 4 1 .S 4 2 .4 5 6 .0 5 5 .4 5 3 .5 4 2 .2 18 4 2 .5 4 0 .8 4 2 .0 4 2 .7 5 6 .5 5 5.7 5 3.7 4 4 .3 21 4 2 .6 4 1 .4 4 2 .0 4 2 .7 57.1 5 5 .8 5 3 .7 4 4.3 28 4 2.6 4 1 .3 4 2 .0 4 2 .8 5 8 .2 5 5.9 5 5.0 4 9 .4 35 4 2 .8 4 1 .5 4 2 .0 4 3 .0 5 8 .9 5 5.9 5 5 .7 4 9.7

a W ater rem oved on basis o f total water present.

Dehydration over alumina and sulfuric acid takes place at nearly the same rate. In the instance of calcium chloride the removal of water from hydrated copper sulfate follows a similar course but is about 5 days slower at the end of any period. On the other hand, phosphorus pentoxide shows less abrupt changes and, although a rapid loss of water starts earlier than over calcium chloride, a constant weight is reached

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October 15, 1930 IN D U STRIA L AN D ENGINEERING CHEMISTRY 357 more slowly. This is explained by the poor diffusion of air

through the phosphoric acid formed on the surface.

In the comparison of barium-magnesium perchlorate with alumina, sulfuric acid, and calcium chloride the course of dehydration over the last three dcsiccants was similar to that of the first test except that it was somewhat more rapid and at the point of substantially constant weight the total loss of combined water was increased from 42 to between 55.7 and 58.9 per cent. The rate of dehydration over barium-magnesium perchlorate was slower than over the other desiccants and after 35 days 49.7 per cent of the com

bined water was absorbed.

F ig u re 2— D e h y d r a t io n o f C o p p e r S u lfa t e P e n t a - liy d rn te o v e r A ctiv a te d A lu m in a , S u lfu r ic A d d , C a lc iu m C h lo r id e , a n d P h o s p h o r u s P e n to x ld e

Changes in W eight of Ignited A lum in a over Various Desiccants

A third method of comparing the efficiency of laboratory desiccants and one which is most exacting is that of cooling ignited alumina. Because of the tendency of ignited alu

mina to absorb moisture, the atmosphere of the desiccator must be maintained at a uniformly low vapor pressure to obtain correct results. In these experiments samples of about 0.5 gram of hydrated alumina were placed in crucibles, ignited 4 hours at 900-1000° C., placed in a desiccator, and allowed to cool for 1 hour. The crucibles were weighed and then each was placed in one of four similar desiccators which were provided with one of the desiccants as shown in Table III. After 1 day and 2 days they were again weighed. Two groups of four crucibles were treated in this manner; the first group was originally cooled over

phosphorus pentoxide, the second over calcium chloride.

Owing to the slight differences in treatment, the groups are not strictly comparable with one another, but the crucibles within any one group were treated similarly and should show variations which are due only to the desiccant. These re

sults are shown in Table III.

T a b le I I I — C h a n g es In W e ig h t o f I g n it e d A lu m in a ov e r V a riou s D e s icca n ts

AliOi PjOj HtSOi CaClj

B a-M g Pbrchlo-

RATB

Gram Gram Gram Gram Gram

Group 1:

W eight after cooling 0.3728 0.3587 0.3452 0.3477 W eight after 1 day 0.3711 0 .3588 0.3441 0.3478 W eight after 2 days 0.3711 0.3585 0.3444 0.3468 T otal change in weight - 0 .0 0 1 7 - 0 .0 0 0 2 - 0 .0 0 0 8 - 0 .0 0 0 9 Group 2:

W eight after cooling 0.3233 0.3242 0.3199 0.3298

W eight after 1 day 0.3231 0 .3246 0.3199 0.3302

W eight after 2 days 0 .3233 0 .3243 0 .3199 0 .3309

T otal change in weight * 0 .0 0 0 0 + 0 .0 0 0 1 * 0 .0 0 0 0 + 0 .0 0 1 1

It is assumed that the closest approach to the true weight of ignited alumina is the minimum weight obtainable and, furthermore, if the weight on standing changes from the original, the slowest increase or the fastest decrease is most desirable. In the first group the greatest loss in weight takes place over alumina and the least over phosphorus pentoxide. In the second group alumina, sulfuric acid, and calcium chloride are very similar in their effects, but over barium-magnesium perchlorate the crucible shows a marked increase in weight.

Other Advantages of Alum ina as a Desiccant From the three series of experiments it is concluded that this new form o f alumina is an ideal desiccant in respect to efficiency. Its other advantages, however, as compared with the more common desiccants may be enumerated as follows: Unlike phosphorus pentoxide, it may be easily handled; it is not dangerous, as is sulfuric acid; it does not deliquesce, as do calcium chloride and sodium or potassium hydroxide; the absorption of moisture does not change the volume or physical appearance of the absorbent; it is reasonably neutral, and does not react readily with most gases and vapors; under ordinary desiccating conditions it will absorb 15 to 20 per cent of its weight of water; it may be reactivated in 6 to 8 hours in an oven at 175° C., and this reactivation may be repeated indefinitely, as the alumina does not deteriorate; finally, it is available in any convenient size and is inexpensive.

Literature Cited (1) Baxter and Warren, J. Am . Chem. Soc., 33, 340 (1911).

(2) D over and Marden, Ibid., 39, 1609 (1917).

(3) Johnson, Ibid., 34, 911 (1912).

(4) M arden and Elliott, J. Ind. Eno. Ch em., 7, 320 (1915).

(5) Smith, Chemist-Analyst, 18, N o. 2. 18 (1929).

(6) Y oe, Chem. News, 130, 340 (1925).

Russia Plans Sixteen Rayon Plants

The Soviet Government proposes to construct 16 rayon plants, costing $125,000,000, with an annual productive output of 35,000 tons, according to Soviet reports received at the De

partment of Commerce. Three rayon mills are already under con

struction and are expected to commence operation next summer.

The productive capacity of the three mills under construction is estimated at between 4000 and 4500 kilograms per day, accord

ing to Soviet information.

Two Soviet trusts have signed 5-year contracts with a German firm for constructing and starting in operation two rayon fac

tories, the German firm to prepare plans for construction, to

give expert opinion, and to turn over to the Soviet trusts licenses for all its patents and processes. The German firm is also to train Soviet engineers and workmen in its German plants, as well as send German specialists to Russia. The equipment will be ordered partly in Russia and partly from abroad. Only domestic raw materials will be used for rayon production in these factories.

The Soviet Government entered into a contract some time ago with Emile Brounert of the "Soieries de Strasburg,” who is also connected with the Union of French Producers of Artificial Silk.

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358 A N A L Y T IC A L EDITION Vol. 2, No. 4

Determination of Boron in Natural W aters and Plant Materials 1

M odification of th e C h a p in M eth o d

L. V. Wilcox

O f f i c e o f W e s t e r n I r r i g a t i o n A g r i c u l t u r e , B u r e a u o p P l a n t I n d u s t r y , W a s h i n g t o n , D . C .

S

ALTS of boron are natural constituents of most of the surface and underground waters of southern California.

The amount present is very small, however, seldom exceeding 5 parts per million of elemental boron. Boron also occurs in measurable quantities in the leaves of many plants— for instance, oranges, lemons, and walnuts.

The writer was unsuccessful in separating these minute amounts from the material with which it was combined by any of the usual methods of boron analysis.

A modification of the Chapin method, however, has been in satisfactory use for two and one-half years and more than two thousand determinations have been made. The descrip

tion of the method may give one the impression that it is tedious, but after the apparatus is set up and solutions are prepared one operator can usually complete eight to twelve determinations per day.

Previous M ethods for Boron

Two groups of procedures have been developed for the determination of boron. One of these involves a series of separations b y fusion, acid digestion, and precipitation, with the final removal of the carbon dioxide by boiling. The methods developed by Wherry (7), Ross and Deemer (6), and Dodd (5) are representative of this group. In the second group boron is separated from the material in which it occurs by means of its volatilization as methyl borate.

The fact that this separation could be made was first pub

lished in 1887 by two investigators, Gooch (4) and Rosen- bladt (5), working independently. In this earlier work the distillate containing the boron as methyl borate was brought into contact with lime or magnesia and the quantity of boron was determined by the increase in weight of that material.

Later investigators using the distillation method substituted various methods of titration for the gravimetric methods o f measuring boron. The investigations conducted between 1887 and 1906 were reviewed and materially improved by Chapin (2) in 1908. The Chapin method was developed for the analysis of minerals. It was subsequently adopted, after thorough investigation, by Allen and Zies (1) for de

termining the boron content of optical glass.

In the present investigation, which has to do with the boron content of water and plant material, methods of both groups were carefully tested and it was finally decided to adopt the Chapin method with some modifications. The method as now used is described in detail in the following paragraphs.

Reagents

Sofnol red No. 1 indicator, 0.4 per cent in 95 per cent ethanol;

or methyl red indicator, 1 per cent in 50 per cent ethanol Phenolphthalein— 1 gram dissolved in 100 cc. of ethanol and

made up to 200 cc. with water Hydrochloric acid— Concentrated c. p. Hydrochloric acid— Approximately 2 normal Hydrochloric acid— Approximately 0.1 normal Sodium hydroxide— Saturated

Sodium hydroxide— Approximately 0.5 normal, carbon dioxide-free Sodium hydroxide— Standard, 0.046 normal (1 cc. is equivalent

to 0.5 mg. of boron) 1 R eceived June 21, 1930.

Mannite— Neutral. U. S. P. quality is usually satisfactory.

Methanol— The water-white synthetic methanol now obtainable has been entirely satisfactory. It is necessary to redistil the methanol over lime before use. The waste methanol can be recovered for use again in the same manner.

Calcium chloride—Granular, anhydrous, and free from boron.

This last requirement is seldom met and the boron found in the blank determinations is usually traceable to the calcium chloride. It is therefore obvious that the same amount of this reagent should be used in the determinations as in the blank.

Apparatus

The set-up of apparatus is similar to that used by Chapin and is shown in Figure 1.

R— Reservoir flask, a 1-liter ring-neck Pyrex flask for methanol.

There should be a safety trap on this flask containing a little mercury. A capillary boiling tube, 3 mm. in bore, the bore closed at 1 cm, from the lower end, will aid in boiling. Calcium carbonate and pumice are used for the same purpose.

B— A 2-liter Pyrex beaker used as a water bath.

D— Decomposition flask, Kavalier glass Erlenmeyer flask of 250 cc. capacity. Inlet tube extends nearly to the bottom.

Kavalier Bohemian glass, according to analysis, contains no boron. This or a similar boron-free glass must be used.

5 — Receiving flask, same size as D, protected with a water trap.

C— Glass tube condenser, tube should be at least 1 cm. inside diameter.

In addition to the apparatus shown in Figure 1, another distilling apparatus is necessary. A 1-liter copper Kjeldahl flask is connected b y means of a 3-hole stopper to a glass condenser. One hole through the stopper carries the tube connecting the flask to the condenser; the second hole carries a mercury trap exactly like the one shown on the reservoir flask in Figure 1; the third hole carries a ther

mometer. Distillation is considered complete when the temperature of the vapor reaches 95° C. The condenser discharges into a 3-Iiter glass flask protected b y a water trap. This apparatus is used to distil off the alcohol after the first separation, see “ Treatment of Distillate” below.

Preparation of Sam ple

W a t e r— Evaporate 2500 cc. to a moist residue in a 1- liter copper beaker, keeping it alkaline to phenolphthalein with saturated sodium hydroxide. Transfer to a 250-cc.

Kavalier glass Erlenmeyer flask, washing the copper beaker finally with 0.1 N hydrochloric acid. This acid may acidify the solution in the flask; if so, make alkaline as before and evaporate to a solid residue. It is not necessary to dehy

drate completely. Acidify with concentrated hydrochloric acid; 5 cc. are usually sufficient. Heat to boiling, but avoid evaporation as boron will be lost. Test with indicator to make sure that the contents of the flask are acid. Add 1 cc. excess acid. Add 10 grams of calcium chloride and 50 cc. of methanol and distil as described under “ Distillation.”

An anhydrous condition must be maintained in the flask or the boron will not be quantitatively distilled over. Roughly, 10 grams of calcium chloride will take care of 10 cc. of water. The contents of the flask must be acid throughout the distillation and it is well to test the acidity at the end with a drop of indicator.

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October 15, 1930 IN D U STRIAL AN D ENGINEERING CHEMISTRY 359

P l a n t M a t e r i a l s —Dry at 70-80° C., grind to a fine powder, and composite. Weigh 10 grams of tiie material and transfer to a decomposition flask, as mentioned above.

Add 80 cc. of methanol, 5 to 8 cc. of hydrochloric acid, and 10 grams of calcium chloride. Distil as described below.

In case there is very little boron in the sample, it is often advisable to use an aliquot of 20 grams. More methanol must be used, as the contents of the flask must be fluid in order to boil freely.

In some instances it has been found desirable to use ali

quots as largc^as 100 grams. In such cases it is best to ig

nite the material to a white ash in the presence of calcium oxide. The ash is then transferred to a decomposition flask, made acid, and distilled as described above.

The operations following the distillation are the same for plant material as for waters and will be described in the following paragraphs.

Distillation

Connect flask D containing the sample as shown in Figure 1.

Flask S should contain 10 cc. of 0.5 N sodium hydroxide to prevent escape of methyl borate. Start methanol distilling from reservoir R. When the contents of D are hot, light a small flame under the flask. Try to regulate the heat so that the volume of the flask D does not change. Distil until 150 to 200 cc. are collected in the receiver S. Rinse the contents of the trap tube info S and treat the distillate as detailed below.

T reatm en t of Distillate

Make the solution alkaline to phenolphthalcin, then add 10 cc. of 0.5 N sodium hydroxide in excess. Transfer to a 1-liter copper Kjeldahl flask, not shown in diagram of ap

paratus, and distil off the methanol. This methanol can be fractionated and used again. Transfer the liquid left in the Kjeldahl flask to a 250-cc. copper beaker, evaporate to dryness, and ignite at a red heat. Add about 10 cc. of water, heat to boiling and, with the aid of a stirring rod having a rubber tip, transfer to a volumetric flask. The writer used the 100- 110-cc. volumetric sugar flasks for this purpose. Add 7 drops of Sofnol indicator.

Note— W e use and recommend Sofnol red N o. 1 indicator for boric acid titrations (manufactured b y Sofnol, Ltd., Greenwich, England).

However, if it is not available, m ethyl red may be used with almost equal satisfaction.

Make distinctly acid with 2 Ar hydrochloric acid. Shake to expel carbon dioxide and then make distinctly alkaline to phenolphthalein with 0.5 N sodium hydroxide. Make up to 110 cc. and filter into another of the sugar flasks. Take an aliquot of 100 cc. of the filtrate, transfer to a 250-cc.

Kavalier flask, and proceed with titration as described below.

Titration of Boric Acid

Make the alkaline filtrate acid to Sofnol with 2 N hydro

chloric acid and then add 5 drops of excess acid. Boil 3 minutes, shaking the flask occasionally to aid in the expul

sion of carbon dioxide. Cool. Titrate as follows: Add carbon dioxide-free 0.5 N sodium hydroxide until a slight yellow color of Sofnol shows. Add 1 or 2 drops of 0.1 N hydrochloric acid. The solution should become pink. Add the standard 0.046 N sodium hydroxide drop by drop until the pink just disappears. The color will be orange not unlike the orange of neutral methyl orange. (If methyl red is used, the neutral color is also' orange.) This is the neutral point for Sofnol and the initial point for titration. Read the buret. Add 1 drop of standard alkali. The indicator should change to a clear lemon yellow. If it does not, one would suspect that carbon dioxide was not completely re

moved. Continue adding the standard alkali until a reddish

color appears, showing phenolphthalein alkalinity. Add about 1 gram of mannite. The red color will be discharged if boric acid is present. This is a very sensitive and useful qualitative test for boric acid. If the red color is discharged, continue adding standard alkali until the red of phenol

phthalein reappears. Add another gram of mannite. The color will probably remain but, if it does not, add more alkali and mannite until a permanent end point is obtained.

This first red color that is permanent in the presence of mannite is the end point of the titration.

The blank is determined exactly as described above, all of the reagents being used. The writer’s blanks range from 0.45 to 0.60 cc. standard 0.046 Ar sodium hydroxide.

Calculations. Cubic centimeters of standard 0.046 N sodium hydroxide used between the initial point and the end point less a blank equals the net titration, which multiplied by 0.5 gives the milligrams of boron in the aliquot. In this titration boric acid acts as a monobasic acid. We use an aliquot of 100/110 of the original sample, so after making this correction the following factors apply:

For 2500-cc. aliquot of water, 1 cc. 0.046 N NaOH = 0.2 p. p. m.

For a 10-gram aliquot of leaves, 1 cc. 0.046 IVNaOH = 50 p. p. m.

Discussion

This method for the determination of boron differs from the Chapin method chiefly in the employment of copper flasks and beakers and of Kavalier Bohemian glass flasks for the hot alkaline solutions. Copper beakers are used for the first concentration of the water sample, which must be kept alkaline to prevent the loss of boron by volatilization.

Copper Kjeldahl flasks are used when separating the methanol from the alkaline distillate, and finally copper beakers are used in drying and igniting the alkaline residues from the Kjeldahls. Tliis ignition appears to be essential in order to oxidize the organic matter of the distillate that would otherwise interfere with the titration. New copper apparatus must be ignited at a high temperature and cleaned thoroughly to remove the lacquer before being used for boron determi

nations.

It is well known that laboratory glassware is measurably soluble in hot alkaline solutions. The writer has found that Pyrex Erlenmeyer flasks, similar to the decomposition flasks, yield approximately 2 mg. of boron when used for the con

centration of 50 cc. of 0.1 N sodium hydroxide. No boron is obtained from Kavalier flasks. Both Kavalier and Pyrex flasks yield silica to hot alkaline solutions, but in the method described the silica dissolved from the Kavalier flasks does not interfere as it remains in the decomposition flask. When copper apparatus is not used the blank determinations are high and erratic, but with copper apparatus consistently low blanks are obtained.

Industrial and Engineering Chemistry : analytical edition, Vol. 2, No. 4

Analytical

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Determination of Boron in Natural W aters and Plant Materials 1

M odification of th e C h a p in M eth o d

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