of m etals and alloys. The perchlorate ion, introduced by the use of perchloric acid as

solvent, is removed before precipitation of the alkaline earth group.

T

cluded in the alkaline earth group which consists of barium, strontium, calcium, and magnesium. The methods follow the scheme of Noyes and Bray (5) with the exceptions of the confirmatory tests for barium and strontium. The working technique and apparatus are essentially the same as those suggested for the separations of members of the third analytical group (S). To facilitate the precipitation of the whole group as carbonates, of strontium chromate, and of magnesium ammonium phosphate the use of the vibrating armature of an ordinary door bell was found to be effective.

The tabular outline shows the general scheme for the sepa­

rations. The numbers of the precipitates and solutions cor­

respond to the numbers of the paragraphs in Noyes and Bray (5) in which the analogous macroprocedures are described.

Procedure

Solution S96 + (NH,)2C 03 + NH,

Precipitate P151 : Solution S151:

BaCOs, SrC03, CaC03) M gC03.(N H $C 03 Alkalies with 25-cu. mm. portions of concentrated hydrochloric acid.

Extract the residue with three 50-cu. mm. portions of water, separating any insoluble residue by centrifuging after each addi­

tion and evaporate the combined extracts over steam in small portions in a platinum crucible. Moisten the residue with 10 cu.

mm, of 6 M ammonium chloride solution and evaporate to dry­

ness. Heat the crucible at 140° C. for 10 minutes. Then place the crucible on a silica triangle and heat cautiously with a small flame until fumes are no longer given off. Finally heat the crucible just to the point of dull redness and discontinue further heating.

Extract the residue with several 10-cu. mm. portions of water, add the solution to a cone, evaporate to dryness, and dissolve in 10 cu. mm. of water. The solution should be clear at this point. If it is not, separate solution and residue by centrifuging.

To the solution add 15 cu. mm. of ammonium carbonate reagent (5) and 15 cu. mm. of 95 per cent ethyl alcohol. If the precipitate is large, add 15 cu. mm. more of each of these solutions. Stir with a glass thread, attach to the vibrator, shake intermit­

tently for 10 minutes, and centrifuge. Remove the solution and wash the precipitate with a little ammonium carbonate reagent.

P r e c ip i t a t i o n o p B a riu m . Add to precipitate P151 in the cone 5 to 15 cu. mm. of 6 M acetic acid and warm on the steam bath until the carbonates are dissolved. Evaporate the acetic acid solution to dryness over the steam bath in a current of air.

To the residue add 10 cu. mm. of water, 10 cu. mm. of 3 M am­

monium acetate, and 2 cu. mm. of 6 M acetic acid. Heat the mixture on the steam bath and add to it, in portions of about 0.3 cu. mm., 3 cu. mm. of 1.5 M potassium chromate, shaking after each addition. If the precipitate is large, add 2 cu. nun. more of the potassium chromate solution. Allow to stand on the steam bath for 5 minutes. A yellow precipitate shows the pres­

ence of barium. Centrifuge and separate solution and precipitate.

Wash the precipitate with a little water and set it aside for later use.Estimate the amount of barium present by comparing the size of the precipitate with a known amount of barium chromate precipitate obtained by treating a solution of barium nitrate in the same manner as the unknown solution.

P r e c ip i t a t i o n op S tr o n tiu m . To solution S i52 which may contain strontium, calcium, and magnesium add 6 M ammonia until the solution turns yellow and then 5 cu. mm. more. Heat in a water bath to 60° to 70° C. and add in three portions 15 cu. mm.

of ethyl alcohol, shaking or stirring after each addition if a pre­

cipitate occurs. If a large precipitate results, add 3 cu. mm. more of potassium chromate solution and 15 cu. mm. of ethyl alcohol.

Cool the solution, oscillate on the vibrator one minute, allow to stand one minute, and centrifuge. Estimate the amount of precipitate as in the case of barium chromate. Separate solution and precipitate, but do not wash the latter.

The necessity of the performance of a confirmatory test for barium depends upon the quantity of strontium found (5). If strontium is either absent or present in a small quantity, forma­

tion of precipitate PI52 is sufficient proof of the presence of barium.

C o n firm a tio n op B a riu m . Dissolve barium chromate pre­

cipitate P152 in a cone with 5 to 10 cu. mm. of hydrochloric acid.

Add 5 cu. mm. of 4 M sulfuric acid, stir, and centrifuge. Remove the solution and wash with three portions of 0.1 M nitric acid to remove all traces of calcium, as these interfere with the later formation of barium sulfate crystals. To the precipitate add such an amount of concentrated sulfuric acid as to form a mix­

ture containing 5 micrograms of barium per cubic millimeter of solution. Stir the mixture, remove 5 cu. mm. of the slurry ob­

tained with a capillary pipet, and place on a slide. Heat the slide over a microDurner until dense white fumes are evolved and allow to cool. If crystals do not appear in a few minutes, breathe oncc or twice over the solution. If crystals are too small, repeat the heating of the test drop as described above. The character­

istic forms of the crystals of barium sulfate and strontium sulfate are shown in the photomicrographs (Figures 1 to 4). Sulfuric acid which has stood in a small reagent bottle for some time should not be used for this test ([4).

C o n firm a tio n o f S tr o n tiu m . T o strontium chromate pre­

cipitate P154 add 25 cu. mm. of 3 M sodium carbonate solution and heat on the steam bath with stirring for 10 minutes. If more than 50 micrograms of strontium are present, repeat the treat­

117

ment with another 25-cu. mm. portion of the sodium carbonate solution. Centrifuge, separate the solution and precipitate, and wash with three 5- to 10-cu. mm. portions of 3 ill sodium carbon­

ate solution. Add sufficient hydrochloric acid to dissolve the precipitate and evaporate in small portions on a slide. Test the residue for strontium by the method of Adams (1). [The nitrite reagent is prepared by mixing equal volumes of potassium nitrite solution and acetate buffer solution. The former con­

tains 500 grams of potassium nitrite in 1 liter. The latter is pre­

pared by adding 450 grams of sodium acetate trihydrate (or 325 grams of potassium acetate) and 100 ml. of glacial acetic acid to sufficient water to make 1 liter of solution. The mixed reagent decomposes slowly, but if kept in a stoppered microcone it may be used for several days.]

Moisten the residue with a solution of cupric nitrate or cupric acetate which contains a quantity of cupric ion equal to five times that of the strontium present. Evaporate the mixture to dryness. When the slide has cooled to room temperature treat the residue with a small volume of the new nitrite reagent (/).

The appearance of small green squares—probably a triple nitrite of strontium, copper, and potassium—confirms the presence of strontium. The use of transmitted light of high intensity is essen­

tial for the recognition of the color of the crystals under the micro­

scope. The green squares of the strontium compound separate a few minutes after addition of the nitrite reagent. Barium, calcium, and magnesium do not give the test. If a nitrite solution containing 1,000 grams of potassium nitrite per liter is used, the strontium test is more sensitive, but calcium interferes by form­

ing a few green crystals. Barium does not form green crystals but interferes with the strontium test if the quantity of barium present is ten times that of strontium.

S e p a r a tio n o f C a lc iu m fro m M a g n e siu m . Add 50 cu. mm.

of water to solution S154, stir, add 3 cu. mm. of 1.5 M potassium oxalate, and unless a precipitate has already occurred, let the mixture stand about 15 minutes. If a precipitate separates, heat the mixture to 70° to 80° C . and add gradually 3 to 10 cu. mm.

more of potassium oxalate solution, adjusting the total volume of the reagent to the size of the carbonate precipitate. Heat for 5 minutes, centrifuge at once, and separate the solution with a capillary siphon. Wash the precipitate with two portions of water. Estimate the amount of calcium present by comparing with a known amount of calcium oxalate.

C o n f ir m a tio n o f C a lc iu m . Dissolve precipitate P156 with such an amount of 6 M hydrochloric acid as to form a solution

Fig u r e 1. Cr y sta lso f Ba r iu m Su l fa t e

1,180 times actual size

Fig u r e 2. St r o n t iu m Su l f a t e Cry stals

800 times actual sire

containing approximately 5 micrograms of calcium per cubic millimeter of solution. Place the solution on a slide and near it place 1 cu. mm. of 4 M sulfuric acid. By means of a glass thread draw a narrow channel of liquid connecting the two solutions.

If calcium is present, a microscopic examination of the test solution will show the gradual appearance of crystals of calcium sulfate dihydrate such as those shown in the photomicrograph.

In very dilute solutions the crystals form only on complete evapo­

ration of the test drop.

D e t e c ti o n op M a g n e siu m , T o solution SI56 add 5 cu. mm.

of 15 M ammonia and 25 cu. mm. of 0.3 M disodium phosphate.

Cool, and allow to stand 0.5 hour with frequent shaking and oscil­

lating on the vibrator. The presence of magnesium is indicated by the appearance of a white precipitate of magnesium

am-Fig u r e 4. Cr y sta lso f N IL M g P 0 4.6H 20 250 times actual size

Fig u r e 3. Cr y st a l s o p CaS0<.2H20

120 times actual size

T a b l e I. T y p ic a l M i c r o q u a l i ta t iv e A n a ly s e s o f A l k a li n e E a r t h G ro u p

Barium Strontium Calcium Magnesium

Present Found Present Found Present Found Present Found Micrograms Micrograms Micrograms Micrograms

Separation in Cone Confirmatory Tests on Slide Limiting propor­tions B a:Sr - 1:1,000 (5) B a:Sr = 1:5 (Ba) C a:B a - 1:40 (Ca) Sr:Ca =» 1:500 (5) Sr:B a = 1:10 (Sr) M g:Ca = 1:50 (Mg)Sr:M g «= 1:500 (5) C a:Sr — 1:40 (Ca) Ca:M g «= betterCa:M g « 1:300 (5) than 1:50 (Ca)

monium phosphate hexahydrate. Centrifuge and compare the volume of precipitate with one of magnesium ammonium phos­

phate hexahydrate obtained from a known quantity of magnesium.

Wash the precipitate once with 95 per cent ethyl alcohol.

C o n f ir m a tio n o f M a g n e siu m . Dissolve precipitate P158 in such an amount of 6 M acetic acid as to form a solution con­

taining 5 micrograms of magnesium per cubic millimeter. Place all or a portion of the solution on a slide and expose to fumes of ammonia. The presence of magnesium is confirmed by the slow crystallization of magnesium ammonium phosphate

hexahy-drate which, when seen through the microscope, has the ap­

pearance shown in the photomicrograph.

About forty solutions were analyzed in accordance with the above scheme and Table I shows eight representative re­

sults, as well as the limiting proportions of the main and con­

firmatory tests if made according to the scheme. In the case of the confirmatory tests, the elements in parentheses indicate those for which the tests are made. The limits of identification were: for separations, approximately 1 micro­

gram; for confirmatory tests, barium and strontium 0.1 microgram, calcium 0.04 microgram (2), and magnesium 0.001 microgram (2).

Literature Cited

(1) Adams, J. I., Benedctti-Pichler, A. A., and Bryant, J. T., Mikro-chernie (in press).

(2) Benedctti-Pichler, A. A., and Spikes, W. F., "Introduction to the Microtechnique of Inorganic Qualitative Analysis,” p.

107, Douglaston, N. Y., Microchemical Service, 1935.

(3) Benedctti-Pichler, A. A., and Spikes, W. F., Mikrochemie, Rare Elements,” New York, Macmillan Co., 1927.

Re c e iv e d October 22, 1938.