H2SO4; i. e., 10 c.c. of the one must exactly neutralize 10 c.c. of the other.

4. Tincture of litmus.

b. Mode of Procedure.

Pour 20 c.c. of normal H2SO, carefully into a Varrentrapp and Wills' nitrogen bulb apparatus. In a strong flask of 100 c.c. capacity, containing a layer of soda-lime 2 c.c. thick, is poured 5 c.c. of urine, and the flask quickly closed with a double-perforated stopper and buried to the neck in a sand-bath. Through one of the perforations a tube leads to the nitrogen apparatus, and the other is supplied with a finely drawn-out sealed glass tube. The sand-bath is heated as long as bubbles pass through the nitrogen apparatus. When these cease the end of the glass tube is broken off, and all the ammonia is drawn from the flask by careful aspiration. Now pour the contents of the nitrogen apparatus into a beaker-glass, wash well with water, add a few drops of litmus tincture, and then add the sodium-hydrate solution from a burette until the red color changes to blue.

If no ammonia had been generated by the distillation of the urine, 20 c.c. of the sodium hydrate would have to be added to neutralize the 20 c.c. of H2SO. If 14 c.c. is however found to be sufficient, we know that 6 c.c. of H2SO, have been satisfied by the ammonia formed. Since 1 c.c. of the acid corresponds to 0.014 grm. of nitrogen, then the total amount of nitrogen which has

gone to form ammonia would be 6+ 0·014=0·084 grm. This would be given off by 5 c.c. of urine. Hence, if we had employed the whole amount of urine excreted in twenty-four hours (say 1,500 c.c.), we would have the amount indicated in the proportion 5:0.084 :: 1,500: x, =25.2 grms., which is the total amount of nitrogen ex

creted in twenty-four hours.

VII.

DETERMINATION OF ALBUMEN.

Pour into a beaker-glass 100 c.c. of filtered urine if a slight amount of albumen is present, or 50 c.c. if a moderate amount is present, or 20 c.c. if rich in albumen. In the second case add 50 c.c., and in the last 80 c.c. of water, and heat for half an hour on a water-bath. Should the albumen not have separated in large flakes, then one or two drops of acetic acid should be added and the heat again applied. As soon as the fluid has become clear it should be filtered through a small plaited filter-paper which has been previously weighed (see uric acid determination, page 210), taking care that all the coagula should be brought upon the filter, if necessary by the aid of a feather, and the beaker washed with hot water. Then the coagulated albumen should be washed into the point of the filter, and further washed with hot water until chlorides can no longer be detected in the filtrate by the AgNO, test. Then dry between watchglasses at 100° until no loss of weight is observed. The determination of the total amount excreted in twenty. four hours is easily calculated from this.

If one has a good polarizing apparatus, the amount of albumen may be easily determined, provided no sugar is present.

Fehling's solution. In 1,000 c.c. there are 34.639 grms. of cupric sulphate, 173 grms. of pure crystalline tartrate of sodium and potassium, and 500 grms. of caustic soda solution of specific gravity 1:12. ("Darstellung," Neubauer and Vogel, 1. c., 206.) Of this solution 10 c.c. are reduced by 0.05 grm. of sugar.*

b. Mode of Procedure.

The determination depends upon the property that grape sugar possesses of reducing the cupric sulphate in the presence of an alkali. For this investigation a small amount of filtered urine is taken which has been largely diluted with water, unless it has previously been ascer tained that only traces of sugar are present. Usually 10 c.c. of urine and 190 c.c. of water are employed. A burette is filled with this mixture exactly to the zero mark. Then 10 c.c. of Fehling's solution are poured

[* This fluid is best preserved by being put into small vials (20–30 c.c. capacity) and kept in the dark. Before using as a quantitative test a portion should be boiled, and if a precipitate occur the liquid should be freshly prepared. The liquid test is preferable to the pellets now on the market.]

into a flask or porcelain dish and diluted with 40 c.c. of water, then heated over a flame, having previously protected the flask with a piece of wire gauze. As soon as the copper solution begins to boil, the urine is added drop by drop from the burette. Soon the fluid becomes yellow, then red, and finally the last trace of the blue color disappears, and the red suboxide of copper rapidly subsides when the source of heat is removed. If allowed to stand for some time, the origi nally blue solution is seen to be colorless, or slightly yellow if more urine has been added than was necessary for the reduction of the copper. The entire loss of color of the fluid is consequently the limiting point of the reaction.

Since with the unaided eye it is not easy to determine when the fluid is colorless* and inclined not to any tint whatsoever, it is advantageous to pass a few drops of the fluid through a small filter and divide the filtrate into two parts, one of which after acidifying with acetic acid is tested for copper with ferrocy anide of potassium, and the other with Fehling's solution for sugar. If by this method we obtain no reaction for either copper or sugar, neither is present in excess, and consequently the limiting point of the reaction has been reached.

In the determination of the amount of sugar, the quantity of urine employed must be known. If 25 c.c.

[* Pavy has modified this test by the addition of ammonia to prevent the precipitation of the red oxide, which renders it difficult to distinguish the point of final reaction. For an account of his method, also called the "ammonio-cupric," see "London Lancet," March 1, 1884, p. 376.]

of the urine mixture were necessary to reduce 10 c.c. of Fehling's solution, the urine mixture being so made up that in 200 c.c. of it there were contained 10 c.c. of urine (the remainder water), then if x amount of urine in 25 c.c. of the urine mixture (the amount employed), we would have 200:10 :: 25:

of urine.

125 c.c.

In this case 1.25 c.c. of the urine was necessary to reduce 10 c.c. of Fehling's solution. Now this solution is so constituted that for the complete reduction of 10 c.c. of the same it is necessary to have 50 milligr. of sugar. Since, however, 1.25 c.c. of the urine has effected this reduction, it is certain that this quantity must have contained 50 milligr. of grape sugar. Hence it is easy to calculate the sugar in the entire amount for the twenty-four hours.

If, for example, a diabetic patient had excreted 5,000 c.c. of urine, we would have 1.25 c.c.: 50 milligr. :: 5,000 c.c.: x=200,000 milligr., or 200 grms. of sugar. If albumen is present, it must be separated beforehand in the usual manner.

2. Knapp's Method.

a. Volumetric Solution.

grms. of

Ten pure dried mercuric cyanide are dissolved in some water; 100 c.c. of sodium hydrate (specific gravity 1.145) are added, and the whole diluted to 1,000 c.c.; 40 c.c. of this solution are reduced by 100 milligr. of sugar.