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B. Hydrofluoric, Oxalic and Silicic acids which are insoluble in acetic acid.

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To the major portion of the solution add conc. aqueous calcium acetate Ca (C2H ̧O2), in very slight excess. A white precipitate shows the presence of one or more members of this group. Filter, wash the precipitate twice with cold water and reserve the filtrate and washings for treatment under the next group.

Treat the precipitate on the filter with acetic acid passing the acid solution through the filter as long as any of the precipitate dissolves. Wash any insoluble residue twice with cold water and treat the filtrate under A and the residue under B.

A.

Divide A into four portions. Note that CN and CO2 are both precipitated by calcium acetate, but the former is more or less soluble in water and both are decomposed by acetic acid, causing effervesence in the case of a carbonate, and giving the odor of bitter almonds with a cyanide (poison).

1. BO2. Evaporate one portion to about one-half its volume and

acidify it with normal HCl. Saturate a strip of turmeric paper with this solution and dry it at a gentle heat. If the strip assumes a pale rose-red color which in turn becomes greenishblack on adding a drop of KOH, boric acid is present.

2. PO. To a second portion add an excess of an ammonium molybdate solution, warm and let stand. A yellow crystalline precipitate shows the presence of phosphoric acid. Arsenic acid gives a similar precipitate.

3. CHO. Evaporate a third portion to dryness, add a drop or so of conc. H, SO1, and again heat. If the residue blackens and yields an odor of "burnt sugar," tartaric acid is present.

Since boric acid redissolves somewhat after being precipitated by calcium acetate, it will be necessary to test for it again under group five.

B.

1. F. Test a portion of the residue which was insoluble in acetic acid as follows: Cover a piece of window glass or a small watch glass with a thin coating of wax and when the wax is cold remove a portion of it with some sharp instrument. Mix the residue to be tested with enough conc. H2SO, to make a paste and cover the exposed parts of the glass with the mixture. Let the test stand for fifteen minutes, then clean the glass and see if it has been etched where exposed. If so, hydrofluoric acid is present. 2. C2O. Place another portion of the residue in a test-tube with a little MnO2 and cover it with H2SO4. While boiling hold in the escaping vapor a drop of clear lime water on the end of a glass rod. If the drop becomes cloudy due to the liberation of CO2, oxalic acid is present.

3. SiO.. Treat a third portion with HCl and evaporate to dryness. Digest the residue with H2O and HCl and filter. A white gritty insoluble powder indicates silicic acid as SiO,.

Group III

This group contains Chromic and Sulphuric acids which are precipitated from the filtrate of group two by Barium Acetate.

To filtrate from Group II, add a slight excess of barium acetate, Ba(C2H3O2)2 and agitate. A fine white precipitate shows the presence of sulphuric acid and in that case, filter and pass to the next group, A fine yellow precipitate indicates chromic acid. If a precipitate forms, filter, wash twice and reserve the filtrate for treatment under Group IV. 1. CrO4. Transfer the precipitate to a test-tube and warm with dilute HCl. Any chromate present will dissolve to a yellow solution, the white sulphate when present remaining undissolved. Filter, wash and confirm the presence of chromic acid by acidifying with acetic acid and adding lead acetate for yellow lead chromate. 2. SO. Any white residue insoluble in dilute HCl or HNO,, confirms the presence of sulphuric acid.

Group IV

This group contains Hydroferrocyanic, Sulphocyanic, Hydroferricyanic, Hydrocyanic acids classified under portion "A," and Hydroiodic, Hydrobromic, Hydrochloric acids, classified under portion "B," which are precipitated by Silver Acetate from acetic acid solutions or by Silver Nitrate from nitric acid solutions.

Strongly acidify the filtrate from the last group with acetic acid, add silver acetate in slight excess and gently warm not boil. Filter, wash twice and reserve the filtrate for later treatment. Divide the precipitate into two portions A and B.

Portion A

Agitate A with a mixture of one part of dilute HCl and three parts of a solution of sodium chloride (1-10) which dissolves the cyanides. Filter and reject the precipitate. Divide the filtrate into three parts.

1. Fe(CN)."". To one portion add FeCl,, as long as a precipitate forms. A dark blue precipitate shows the presence of hydroferrocyanic acid. Filter.

2. CNS. If the filtrate from (1) has a blood-red color, which is destroyed by HgC12, sulphocyanic acid is present.

3. Fe(CN)". To a second portion add a crystal of FeSO, or a freshly prepared solution of FeSO.. A dark blue precipitate shows the presence of hydroferricyanic acid. Or the filtrate from (1) may be boiled with H.SO, and more FeCl, added. A dark blue precipitate shows the presence of the acid.

4. CN. To a third portion add a little picric acid, and an excess of NH,OH and warm. If on standing a light or dark mahogany color appears, hydrocyanic acid is present.

Portion B

Place portion "B" of the precipitate in an evaporating dish with a few pieces of zinc, cover with water, add a few drops of H2SO, and gently warm. When the reduction of the silver salts is complete, indicated by a black precipitate, filter and reject the precipitate. Neutralize the filtrate with Na,CO,, filter, reserve the filtrate and reject the precipitate.

1. I and Br. Test a portion of the filtrate as follows: Add to the test an equal volume of CS,, and then nitro-sulphuric acid (1:1) drop by drop, vigorously agitating after the addition of each drop and noting the color of the CS2. If the latter becomes pink or violet, HI is present; if yellow, yellow-brown or red-brown, HBr is present. The iodine is first liberated and the colored sulphide may be removed by filtering. To the filtrate add more CS, and repeat the operation. When all the I has been removed and liberated Br will in turn color the CS.

2. Acidify a second portion of the solution with HNO, and add AgNO, in slight excess. Filter, wash, reject the filtrate and boil the precipitate with an excess of "sesqui" ammonium carbonate. Decant the clear liquid, add a fresh portion of the carbonate and again boil. Decant as before and to the decanted liquids add enough HNO, to acidify. The formation of a white curdy precipitate shows the presence of hydrochloric acid. (Hager's Test.)

In the absence of HI and HBr, add to the test solution AgNO3. A white curdy precipitate which is insoluble in HNO, and which readily dissolves in NH,OH, shows the presence of HC1.

I.

Note 1. When AgNO, is used as the group reagent, the procedure is unchanged except that HNO, must be detected in Group I. Interfering acids are nitrous, chloric, ferro and ferricyanic, sulphocyanic and the halogen acids.

Group V

This group contains Arsenious, Chloric and Nitric acids which are not precipitated in the preceding groups, being soluble.

1. CIO,. To a minor portion of the filtrate from the last group, add a piece of zinc, a few drops of HNO, and gently warm. A white curdy precipitate of AgCl shows the presence of chloric acid. Or to a portion of the filtrate add a little formalin, a few drops of HNO, and heat, a white curdy precipitate shows the presence of HCIO,. In both these tests there must be present an excess of the silver salt.

Remove the silver from the main portion of the filtrate from Group IV by adding a solution of NaCl as long as a precipitate forms. Filter, wash, reject the precipitate and test the filtrate as follows:

2. AsO3. Acidify the filtrate with acetic acid and saturate it with H,S. If a yellow precipitate forms at once, arsenious acid is present. Filter, wash, and treat the filtrate under 3. (Omit test if arsenic was found in the analysis of the metals).

3. Concentrate the filtrate to a convenient volume, and in case chloric acid is absent, apply the "brown ring" test directly. Add an equal volume of conc. H2SO, to the test, so that the two liquids will not mix, cool and pour down the side of the tube some FeSO, solution. Let the test stand for some minutes undisturbed. The formation of a brown or dark brown ring at the juncture of the acid and the test solution, shows the presence of nitric acid. Nitrous acid gives the "ring" with acetic acid in płace of H2SO. 4. To detect HNO, in the presence of HCIO,, acidify the concentrated filtrate, or a portion of it from 3 with acetic acid, boil for a minute with an excess of H2SO,. Filter if necessary, reject any precipitate and to a portion of the clear liquid add a drop or two of diphenylamine in conc. H,SO,. If a blue color appears at once, HNO, is present. This color slowly disappears.

This test depends upon the action of the sulphurous acid in changing any chlorate present into a chloride. To determine whether all the chlorate has been changed, add to the remaining portion of the solution a drop or two of anilin, and then a few drops of conc. H2SO. A blue color appears at once if any chlorate is present in which case use more of the H2SO,. The appearance of a blue color with this test serves to detect a chlorate in the presence of a nitrate. The anilin test gives with a nitrate a yellow-brown color.

5. BO2. To another portion of the filtrate apply the test for boric acid given under Group II. A. (1).

AN EXPERIMENT IN THERMAL CONDUCTIVITY

PROFESSOR H. L. CURTIS, MICHIGAN AGRICULTURAL COLLEGE

The thermal conductivity K of a body is defined from the equation H=KA — T, where H is the quantity of heat in calories which will

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pass in time T between the two faces of a wall of area A, of thickness d, and whose faces are at a temperature and '. It would seem that the most simple method of measuring conductivity is to proceed directly

from the defination and measure the heat flowing through a given wall. I was aware that attempts had been made to keep one side of a wall at the temperature of melting ice, and the other at the temperature of boiling waer by passing steam against it, and that these attempts were unsuccessful, because a coating due to the condensation of the steam would form over the surface which would keep its temperature considerably below that of the steam. However, I reasoned that if I used hot water in the place of the steam and measured the rate of cooling of the water I would have overcome the difficulty.

Accordingly I secured two vessels, one of copper and the other of aluminum, whose conductivities I wished to determine. I filled a large pail with crushed ice and water and arranged to stir it thoroughly. I filled the aluminum vessel with a known amount of warm water and suspended it so that the bottom just touched the ice-cold water. I then read the temperature every 30 seconds while keeping the water well stirred. I then attempted to determine the conductivity as follows:

In a short interval of time, say 30 seconds, the change in temperature of the upper face will be from 0 to 0". The quantity of heat conducted across will be M (0'- 0") where M is the mass of the water. The temperature of the upper face may be taken as the mean of the two. Substituting in the formula for conductivity M (0'-0")=K_A 0'+0" T, since 00°C. A somewhat simpler formula can be obtained 2d by integrating the differential equation which expresses the conductivity, but that solution would be out of place here.

The results obtained by this method were very much too small. As the only error of great magnitude must be in the temperatures of the two faces, I determined to examine into this. For that purpose I had made two vessels identical, except that the bottom of one was of a different thickness from the other. My experiments had caused me to conclude that there is a surface film of water through which the heat must be conducted, the film not being disturbed by the stirring. If this is the case, the following considerations will hold:

Let A and B be sections through the two plates of which the bottoms of the vessels are made. In these d and d' represent the thickness of the two metals, above and below which are the films of water. Let the temperatures of the different surfaces be as represented. When the temperature gradient in the metals of A is the same as that in B., i. e., when

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the same quantity of heat will flow in a unit of time through unit crosssection of the two plates provided the thickness of the films on the

two plates is the same, and they have the same conductivity. We will then measure the flow of heat

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