After intense heating, observe whether the powder is entirely consumed, or whether a residue remains; further, whether the powder is consumed with a visible flame, whether it decrepitates (oxalate of lime), or whether it gives off a characteristic odor.

I. If the powder is entirely consumed by heat, the following stone constituents may be present: Uric acid, urates of sodium and ammonium, xanthine, proteine, and cystine.

(1.) Proteine (fibrine) burns at a red heat with a brilliant yellow flame, and diffuses a strong odor of burning feathers or hair.

(2.) Cystine burns with a weak bluish-white flame, and gives off a penetrating smell like burning fat and sulphur. The powder is dissolved in dilute ammonia, and shows under the microscope, upon evaporation of the same, beautiful hexagonal plates.

(3.) Xanthine by the murexide test shows an orangeyellow color, and burns without a visible flame.

(4.) Uric acid and sodium and ammonium urates burn without visible flame, and give with ammonia a beautiful red, and with KOH a beautiful violet murexide.

a. The urate of sodium is distinguished from the urate of ammonium, and from free uric acid, by the fact that on the foil upon which it has been heated there remains a light cloudiness. If a piece of red litmus paper is moistened with distilled water and laid upon this cloudy spot, a similar blue spot appears on the paper. This is caused by the sodium carbonate (or

caustic soda) which has been formed by heating the urate of sodium. The urate of ammonium and the free uric acid do not give this test.

b. The urate of ammonium is distinguished from the free uric acid by the so-called cold ammonia test. This is accomplished as follows: Take a small test-glass, and to 0.1-0.2 gramme of the powder to be tested add a few drops of a concentrated solution of KOH. This glass is then covered by a watch-glass which has on the convex surface a small piece of wet red litmus paper; if after a few minutes the paper becomes blue, ammonia is

ent.

pres

c. Free uric acid gives naturally a negative result with the litmus test.

II. If the powder is partially consumed, or is unaltered by heat, the stone consists essentially of calcium and magnesium salts. Then the following constituents may be present: Calcium oxalate, calcium carbonate, calcium phosphate, and ammonio-magnesium phosphate.

(1.) Calcium oxalate does not effervesce upon the addition of a drop of HCl. By intense heat this powder shows a peculiar glow and decrepitates slightly. The oxalate of calcium is by this means transformed into the carbonate of calcium; and if now a drop of HCl is added there ensues a brisk effervescence.

(2.) Calcium carbonate effervesces upon addition of HCl without first heating. (By this it is distinguished from the oxalate.)

(3.) Calcium phosphates and the ammonio-magnesium phosphates do not effervesce upon the addition of

a drop of HCl, either before or after incineration. (By this they are distinguished from the carbonate and oxalate.) The incinerated powder is readily soluble in HCl. If we add to this solution ammonium hydrate [(NH)OH] drop by drop until the solution has be come alkaline, there appears a white flocculent precipi tate, which consists of the amorphous basic calcium phosphate and the crystalline ammonio - magnesium phosphate. Under the microscope the triple phosphate appears in stars or oblique crosses, while the calcium phosphate appears amorphous. Accordingly, from this precipitate we may conclude whether the calcium or the ammonio-magnesium phosphate is predominant by the relative amounts of the amorphous and crystalline precipitates.

CHAPTER IV.

REAGENTS AND APPARATUS FOR THE APPROXIMATIVE DETERMINATION OF THE CONSTITUENTS OF THE

URINE.

REAGENTS.

SINCE the physician generally procures his reagents from the apothecary, for the sake of convenience we give the prescription formulæ. For these reactions it is best to employ glass-stoppered bottles with wide necks, with a capacity of 250 c.c.

A. Acids.

1. Acid hydrochloric, concent., c. p., 200 grms.
2. Acid sulphuric, concent., c. p., 200 grms.
3. Acid nitric, concent., c. p., 200 grms.

4. Acid acetic, concent., c. p., 200 grms.

B. Bases and Salts.

5. Potass. caust., p., alcohol dep., 100 grms.
Aqua dest., 200 grms.

6. Ammon., c. pur., liquid, 100 grms.

7. Barii chlorid. cryst., 30 grms.
Aqua dest., 200 grms.

Acidi hydrochlor., 10 grms.
8. Plumb. acet. cryst., 30 grms.
Aqua dest., 200 grms.

9. Cupri sulphat., 30 grms.
Aqua dest., 200 grms.

10. Magnes. sulphat.,

Sal ammoniac, depurat.,

Aqua dest., 200 grms.

ǎā 30 grms.

Ammon. c. pur., liquid, 50 grms.

11. Argent. nitrat., 5 grms.

Aqua dest., 40 grms.

For the latter reagents a pipette is advantageous.

12. Red and blue litmus paper in strips.

Besides these necessary reagents, the following may be employed for special cases: Distilled water, ferric chloride, basic acetate of lead, mercuric nitrate, basic nitrate of bismuth (magist. bismuthi), fuming nitric acid, potassium nitrite, starch, chloroform, ether, alcohol, iodine in iodide of potassium solution, acetic acid, sodium chloride, and zinc chloride.

APPARATUS.

1. Six test-tubes, with rack.

2. Ten wine-glasses or small test-glasses.

3. Cylinder glasses of 100, 200, and 300 c.c. capacity.