more than sufficient to make up this quantity, it is excreted by the urine. If, on the other hand, an insufficiency of chlorin is used, the deficiency will be found in the urine. In poisoning with phosphorus or with carbon monoxid the amount of chlorin in the urine is diminished; and this also takes place in febrile affection, such as pneumonia, which are not attended with the formation of diarrheas or exudates.

A rough approximation of the amount of chlorin in the urine may be made by adding a drop of a 12 per cent. solution of silver nitrate to 10 c.c. of the urine. If the chlorids be present in excess, a heavy clotty precipitate will form; if the chlorids be diminished, the precipitate will be less coherent, or in marked cases only an opalescent precipitate will appear.

The Phosphates in the Urine.-The salts of phosphoric acid present in the urine are those of the alkalies and the alkaline earths. The amount of phosphoric acid in the urine varies between somewhat wide limits.

The amount excreted per diem by the urine is from 1 to 8 grams. The average is about 3.5 grams. The phosphates are, as the chlorids, a direct result of the amount of phosphoric acid taken in with the food. As the salts of phosphoric acid in the urine are principally the monocalcium and monomagnesium salts, which have an acid reaction, it is to these that the acid reaction of the fluid is due. The quantity of phosphates, except in phosphatic diabetes, has relatively little diagnostic significance.

The Estimation of Phosphates.-The solutions required for the estimation of phosphates:

I. Standard Solution of Sodium Ammonium Phosphate.-Dissolve 14.718 grams of this salt in water, and make up to 1000 c. c. Each cubic centimeter of the solution corresponds to 0.05 gram of P2O5. The crystals must be well formed, and dried by pressing them between folds of filter-paper.

2. Standard Solution of Uranium Acetate.-As uranium acetate is a deliquescent salt, it is impossible to weigh it out directly. Dissolve 40 grams of crystallized uranium acetate in 1100 c.c. of water to which 50 c.c. of acetic acid have been added. The mixture is filtered and allowed to cool. Fifty c.c. of the standard phosphoric acid are placed in a beaker, and diluted to 150 c. c. with water. The solution is heated to boiling over a wire gauze. The uranium solution is then added from a burette. Combination of the uranium salt with the phosphate takes place according to the following equation,

NaNH,HPO, + UO (C,H,O,), =
UO,NH,PO + NaC2H2O2 + C2H ̧O2

uranyl ammonium phosphate being formed.

If, before all the phosphate has combined with the uranium acetate, a drop of the mixture be taken out and touched to a drop of a solution of potassium ferrocyanid, no coloration appears. If the faintest trace of the uranium solution be present in excess, a brown color will appear of uranium ferrocyanid. There is thus a method of telling when the uranium solution is present in excess.

Should the uranium solution be exactly equal to the phosphate solution, 50 c.c. would be required to bring about the end reaction. Usually the amount will be less than this, and consequently the amount of solution used from the burette must be diluted to 50 c. c.

Example.-Took 50 c.c of standard phosphate solution, and diluted with 100 C. C. of water. Heated to boiling, and added the uranium solution slowly. 48.5 c. c. were required before the ferrocyanid solution was turned brown. c.c. must be diluted with 50.0

1000 c. c. must be diluted with

Therefore 48.5 48.5= 1.5 c. c., and 1000 X 1.5 48.5

=25.6

C. C. Each cubic centimeter of the uranium solution now corresponds to 0.05 gram of P2O5.

The estimation of phosphates in the urine is carried out in precisely the same manner.

Fifty c.c. of urine are diluted with 100 c.c. of water and heated to boiling, and while in this condition the standard uranium solution is delivered from a burette, the solution being tested from time to time by taking out a drop with a glass rod and touching with a drop of potassium ferrocyanid on a glass plate. When the reaction is given the process is stopped, and the amount of uranium solution read off. In order to obtain the percentage of phosphoric acid in the urine, it is only necessary to divide the number of c.c. of the uranium solution used by 100. Should the urine be strongly alkaline, it is advisable to render it acid with acetic acid before starting the titration.

Total Solids.-The total amount of solids in the urine may be obtained by evaporating 10 c.c. of the urine to a syrup in a weighed porcelain dish, and finally in an oven heated to 60° C. till a constant weight is obtained. On subtracting the weight of the dish from the total weight of the dish and solids, the amount of solids in 10 c.c. of the fluid will be given. This multiplied by 10 will give the total solids per cent.

It is undesirable to dry the residue at 100° C., because a certain amount of decomposition takes place which interferes with obtaining a constant weight.

The amount of solids may also be estimated from the specific gravity by means of Häser's coefficient. If the last two figures of the specific gravity be multiplied by 0.233, the amount of solids per cent. will be given.

Assuming the normal specific gravity of the urine to be 1020, the percentage of solids would be 20 x 0.2334.6 per cent. With the total amount of urine excreted per diem as 1500 c. c., the total solids will be 1500 × 4.66 = 70 grams. The amount of solids usually assumed to be excreted in the twenty-four hours is 60 grams. This amount would place the normal specific gravity at 1017, supposing the total amount of urine excreted to be 1500 c.c.

Urea.-Urea is the chief nitrogenous constituent of the waste products which is excreted by the kidneys, and it is of correspondingly great importance from a diagnostic point of view. Just what the exact processes are which transform protein

substances into a simple compound like urea are not known, but experimental evidence goes to show that the change takes place in the liver. The quantity of urea passed by the kidneys in the twenty-four hours is roughly 30 grams. An exclusively nitrogenous diet increases it, while any pathologic change in the excretory function of the kidney diminishes it. Hence it is that in cases of

FIG. 23.-1, 2, Urea; 3, smaller scales or rhombic plates of urea nitrate; 4, hexagonal plates.

nephritis the total amount is always less than in health. When metabolism is taking place rapidly, as in fevers, the amount is increased.

Urea itself is a colorless crystalline solid, occurring in stout needles, or in four-sided rhombic prisms (Fig. 23). It is exceedingly soluble in water, and on this account cannot be isolated from the urine alone. It is a very reactive substance and