nution of the quantity of urine is accompanied by, and therefore pathognomonic of, a constant increase in the intensity of the disorder. When the quantity of urine remains very low (below 800 c.c., 253 fl. oz., per day) for any length of time, then we may conclude that the intensity of the disease has not abated. A constant increase in the quantity of the urine, however, is a favorable symptom, and shows that the patient has passed the acme, and that the diseased action is abating (vide Vogel, loc. cit., p. 226). During the period of convalescence the quantity of urine becomes normal, or exceeds in some cases the normal quantity.

Professor Vogel observed the following case, illustrative of these points. It is the more interesting, as the normal quantity of the urine discharged by the patient during health had been measured for a certain period just before he became ill. He was an attendant in the hospital, and became the subject of typhus fever. During the first three days of the illness, the total quantity of urine in twenty-four hours, amounting to 1800 c.c. (58 fl. oz.) during health, fell gradually to 200 c.c. 6 fl. oz.): it rose during the next five days regularly up to the normal 1800 c.c. (58 fl. oz.), exceeded the amount soon up to 2200 c.c. (703 fl. oz.), and then returned gradually to the usual average quantity.

When a disease, acute or chronic, takes a fatal turn, the quantity of urine becomes frequently very low, or remains in a fluctuating low state. This is the case in all diseases ending with or by exhaustion of the material of the component parts of the body. In cases, however, the fatal termination of which is due to a more sudden interference with the powers of the nervous system, or with the mechanical action of the lungs and heart, the quantity of the urine is not usually very much diminished.

The quantity of urine is materially diminished in dropsical diseases, with or without diseased kidneys. Common practice has made the amount of urine discharged by such patients the index of their improvement or otherwise, and has made a small quantity of urine, in cases in which the cause of the disorder is not the kidney itself, a therapeutical indication for the administration of diuretics.

The quantity of the urine is materially increased in those diseases which we commonly term diabetes. In these cases, however, as in cases of diseased kidneys, it is necessary to give particular attention to the quality of the urine at the same time, when the distinctions between hydruria, diabetes insipidus, and diabetes mellitus will become prominent.

SOLIDS AND WATER-SPECIFIC GRAVITY.

The direct way of determining the amount of solids contained in a given quantity of urine is by the evaporation of the water. This is best done under the receiver of the airpump, care being taken not to make the urine boil, in order to prevent loss from the bursting of the bubbles evolved. By placing with the urine to be dried any body capable of freely absorbing water, such as sulphuric acid or quicklime, the vapour may be absorbed as soon as evolved, and in this way a vacuum for air and vapour may be kept up, under the influence of which the urine will rapidly get dry. When nearly dry, the residue may be mixed with a weighed quantity (1 to 2 grammes, 15 to 30 grains) of finely ground spongy platinum. This makes the drying considerably easier.

The vessel in which the urine is exposed should be rather flat, so as to give the largest possible surface for evaporation, and should be provided with ground edges, so that it may be rendered air-tight by greasing them and applying a glass disc. This caution is required in order to prevent the residue from absorbing water from the air, on being transferred from the receiver to the scales for weighing. The weight is now determined in the closed box of the chemical scales, the air surrounding which is kept dry by the presence of sulphuric acid and chloride of calcium. Then the vessel with the residue is again removed to the receiver of the air-pump; after it has been exposed for a time to the evaporating influence, the covered vessel is again weighed; and if it have lost nothing during the last exposure, the residue is considered to be perfectly dry. Of course, if it have lost in weight between two weighings, it must yet be brought repeatedly into the vacuum, until the weight remains stationary.

This process is one of extreme difficulty and great expense of time; but it is the only one which gives accurate absolute results. Less accurate is the following method, in which the evaporation of the water is effected by the assistance of heat. The objection to the application of heat in this process is, that it decomposes a certain amount of urea, which is volatilized in the form of ammonia and carbonic acid. objection is so well founded, that if the products of evaporation are caught in a cooler, it will almost always be possible to find traces of ammonia in the condensed distillate by the delicate test I shall describe under Ammonia. This ammonia, of course, must not be confounded with the ammonia

This

proper of the urine. By always keeping the urine acid

during evaporation, the decomposition of urea may be limited to a minimum; but alkalinity of the urine will favour the destruction of urea during the application of heat. However, where no air-pump is at hand, and where ordinary results only are required, the method now to be described is still of considerable use.

The operator pours about 12 or 15 grammes (or 4 to 5 drachms) of urine by weight or measure into a porcelain or platinum capsule, which, with a well-closing cover, has been counterpoised beforehand. It is then fitted into the ring of the water bath, so that the greater part of its outer surface is surrounded by the hot water.

If the solids only are to be determined, the best plan is to take a flat, small evaporating dish for the operation. The best vessel for a water bath is a semi-globe of copper, with handles, and with rings on the top to fit every size of evaporating dish, and with an opening for replenishing the supply of water. Another water-bath is that which combines the advantages of the one just described with those of an air-bath warmed by water. The top is provided with four holes, admitting as many evaporating dishes or capsules of different sizes. Any hole not used is closed by its cover. The warm air-bath at the front has two compartments, a door, with a rosette for admitting air if required, a ventilator at the top for carrying away the moisture, and an opening, into which a thermometer may be fixed with a cork, if it be desired to keep the temperature at a certain point.

When the urine has evaporated to an apparently dry residue, the capsule must be transferred to an air-bath,—a round box of copper, with double walls and a lid on its upper surface. The substances to be dried are placed upon a sieve of perforated copper, which is placed in the interior of the box in such a manner as to prevent any heat conducted by the metal, particularly the bottom, from reaching the substances. Thus they can only be affected by the hot air, the temperature of which is ascertained by a thermometer, placed with its bulb inside the box, and surrounded outside by a glass tube, in order to prevent the small column of mercury from being affected by any external currents of air.

The capsule being in the air bath, the air is now heated with a spirit- or gas-lamp, under the box, to 230° F. (110° C.), and is kept at that temperature from half an hour to an hour. Being ready for weighing, the capsule is covered, and allowed to cool over sulphuric acid, in the apparatus in which it is carried to the scales. This apparatus is a strong cylindrical glass with ground edges, containing about an inch in depth

of strong sulphuric acid. Over this, the capsule is placed upon a tripod made of strong lead wire. The glass is closed by a glass disc, with the assistance of a little tallow.

After the weight of the capsule and contents has been ascertained, it is again exposed to the temperature of 230° F. (110° C), and if, after some time, a second weighing does not show a further loss, the residue may be considered as dry.

We now find by easy calculation the amount of water evaporated, and the amount of solids contained in a given quantity of urine. If the total quantity of urine discharged in twenty-four hours be known, the total of solids discharged therewith is readily found: for the quantity of urine (u) taken for evaporation stands to residue (r) found, in the same proportion as the total quantity of urine (U) discharged in twentyfour hours stands to the (R) solids dissolved in it.

ur: U: a; hence x =

Ur

น

= R.

For example, let the quantity of urine experimented on be 10 grammes, the quantity of solid residue in it 0.23 grammes, the total quantity of urine discharged 1000 grammes, then

the total quantity of solids dissolved in the urine.

As the urine is a solution of several substances in water, their amount, viz., the amount of solids contained in any given quantity, may be ascertained by finding the specific gravity; for the specific gravity of any watery solution is higher than pure water in proportion to the amount of solids dissolved, the solids in solution giving up their own individual specific gravity, and influencing the specific weight of the solution by their absolute weight only. This is proved by the fact already mentioned; namely, that the absolute weight of a given bulk of urine may be found by multiplying the bulk, as expressed in cubic centimetres, by the figure expressing the specific gravity (p. 20).

The best mode of discovering the specific gravity of the urine is to compare the weight of a certain bulk with the weight of an equal bulk of water. For this purpose any phial of convenient size may be used; but best of all vessels is the pycnometer, a small glass bottle, the elongated ground in stopper of which is a capillary tube. The advantages thereby obtained are, that no air can be inclosed in the bottle (certainly not, as some fancy, because the air, when included, can escape by the capillary tube, which it could not,

from its great adhesion; but because no air is ever inclosed, being displaced by the rising water when the stopper sinks into the full bottle); and that the bottle can be accurately filled with the same bulk of fluid every time. The larger and better kinds of pycnometers are, moreover, provided with a thermometer, the bulb of which lies in the body of the stopper, and the tube in the elongation.

The weight of the pycnometer, and of the water required to fill it, being each ascertained, are written upon the glass with a diamond. The weight of the urine required to fill the pycnometer is then ascertained. Then the weight of water: weight of urine specific gravity of water: specific gravity of urine.

Or, the specific gravity of water being 1,

weight of urine

=

weight of water = spec. grav. of urine.

Ex. A pycnometer held 50 grammes of water, and 5′21-5 !^ grammes of urine.

51.2

50

Or, 50 51.2 ::

1024 spec. grav. of urine;

Another and more convenient mode of finding the specific gravity of the urine is founded on the fact of immersed solids displacing a bulk equal to their own. For this purpose a solid glass ball is used, the loss of which, when weighed in water, is known, and inscribed on it with a diamond. It is then weighed while immersed in urine, and its loss, as compared with its weight in air, is ascertained. Then its loss when weighed in the urine, divided by its loss when weighed in water, will be the specific gravity required.1

Ex. A glass ball lost 500 grammes when weighed in water, and 512 when weighed in urine.

Though the two methods last described do not require so much time and weighing as the first two methods, still they

'Bird and Brooke, Nat. Philos.' p. 193, § 378.