cork.

4. A graduated glass.

5. A 100 c.c. flask, with a glass tube through the

6. A wash-bottle for distilled water.

7. A urinometer.

8. A spirit lamp.

9. Two small porcelain evaporating dishes.

10. A ring stand with two rings.

11. Filter paper.

12. Four glass funnels for filtering.

13. Glass rods.

14. A microscope with appurtenances.

15. A large beaker of 3,000 to 4,000 c.c. capacity.

For special cases we must have watch-glasses, beakerglasses, and pipettes; and for quantitative examination, a delicate pair of scales.

CHAPTER V.

QUANTITATIVE DETERMINATION OF A FEW OF THE CONSTITUENTS OF THE URINE.

As a first step toward the quantitative investigation, the entire mass of the excreted urine must be collected for a given time. Usually the amount for twenty-four hours is collected, but it must be observed that before a stool one should urinate, that none be lost by being mixed with the fæces. It is inadmissible to attempt to determine the amount for twenty-four hours from the quantity collected in one hour (p. 36).

The urine should be collected in graduated cylinders. For large amounts one may graduate a vessel himself. Take a flask containing 1 litre of water at 15° C., and pour into the cylinder to be graduated, making a mark on the glass at the surface of the fluid, repeating this as often as necessary.

If one desires to ascertain the mean amount of the urine excreted by an individual, the total amount should be collected for several days, and the quantity be divided by the number of days.

I. ESTIMATION OF THE DEGREE OF ACIDITY.

In order to ascertain the degree of acidity of the urine, we add Na OH to the same until it reaches the point of neutralization, and then compute how much acid (we usually employ oxalic) is required to neutralize the quantity of sodium hydrate used.

a. Volumetric Solution.

We employ a one-tenth Na OH solution, which in 1 c.c. contains 0.0031 grm. Na2O, which is sufficient to neutralize 0.0063 grm. of crystallized oxalic acid. If we employ normal sodium hydrate, we add 10 times its volume of distilled water. (Description of normal sodium hydrate, Mohr, "Titrirmethode," 4th edition, p. 83.)

paper

b. Example.

We pour exactly 100 c.c. of urine into a beaker-glass, and add while stirring the sodium-hydrate solution drop by drop from a burette, until a drop of the urine on red litmus shows no blue and on blue litmus paper no red spot. The number of c.c. of NaOH solution added (say 14) we multiply by 0.0063, and the product (0.0882 grm.) shows the acidity of 100 c.c. of urine expressed in crystallized oxalic acid.

II. ESTIMATION OF THE SOLID MATTERS.

In order to estimate the solid matters, we take 10 c.c. of urine in a weighed porcelain dish, and evaporate

on a water-bath to dryness. It should then be kept for an hour in a drying chamber at 100°, and then allowed to cool in a desiccator. We now weigh and replace the dish in the drying chamber, weighing again at the expiration of an hour after cooling as before, repeating this until there is no variation in weight. The difference of weight between the empty dish and that containing the solids is the weight of the solid matters in 10 c.c. of the urine. Unfortunately the result is always too small, for the action of the acid sodium phosphate on the urea at this temperature decomposes the latter, and ammonia and carbonic acid are driven off at the same time with the water.

It is seldom that the physician employs this means for the investigation of the amount of solids, for by using Häser's or Trapp's coefficients as satisfactory results are obtained, at least for him. (See p. 39.)

III. ESTIMATION OF UREA.

Liebig's Method.

a. Reagents.

1. Baryta solution.—One volume of a cold saturated solution of barium nitrate is mixed with two volumes of a cold saturated barium hydrate solution.

2. Volumetric mercuric reagent.-This is a solution of mercuric nitrate (in which there must be no basic salt or mercurous compound), of such concentration that in 1,000 c.c. of the solution 71:48 grms. of pure mercury

or 77.2 grms. of pure mercuric oxide (dried at 100°) are contained. See Neubauer and Vogel, 1. c., 183; Mohr, 1. c., 48, 1.)

3. Sodium carbonate solution.-For Raudenberg's modification we employ sodium-hydrogen carbonate.

b. Method of Procedure.

We take up 40 c.c. of urine in a pipette, and add 20 c.c. of the baryta solution. Here, as in all other cases of quantitative work, the greatest care must be exercised. In the pipette there should be no foam, and one should read the division mark on the pipette which corre sponds to the lower edge of the meniscus. We must be especially careful that none of the fluid be lost. If we have treated the urine with the baryta solution, the precipitate of phosphates and sulphates which has separated should after some time be filtered off, using a dry filter-paper and allowing the fluid to run through into a dry beaker. The filtrate is therefore one third baryta solution and two thirds urine from which the sulphates and phosphates have been removed. We now take 15 c.c. of this clear fluid by using a pipette, and allow it to flow into a dry glass vessel. This contains 10 c.c. of urine. Now, from a burette filled precisely to the zero point with the mercuric nitrate mixture, we add about as many cubic centimetres of the mixture as are denoted by the last two figures of the specific gravity of the urine (i. e., 15 c.c. if the specific gravity is 1.015), and try whether the limit has been reached. For this