Albumin is not a normal constituent of urine and when it is present continuously and in any considerable quantity it constitutes a grave symptom. When present, it is in solution, and hence is not at all evident to the eye until it has been coagulated by the action of heat or some other agent. In testing a sample by heat a test tube is half filled with perfectly clear urine and heat is applied to the upper part of the liquid until boiling occurs. If the boiled urine becomes turbid in the least degree, the turbidity is due either to the presence of coagu lated albumin or to the precipitation of the phosphates of lime and magnesia that are nor mally present in all urine. The earthy phos phates promptly redissolve upon the addition of a few drops of nitric or acetic acid; but if the turbidity is really due to albumin it does not pass away upon this treatment. The object of heating only the top part of the test tube hold ing the urine is to facilitate the recognition of a precipitate, a comparison of the upper and lower parts of the test tube, in a good light, rendering the slightest loss of transparency quite visible. If no precipitate is obtained, a drop or two of nitric acid should be added and the boiling repeated. A number of trials of this sort should be made, the nitric acid being added, a few drops at a time, until a consider able quantity of it is present. The consistent absence of a precipitate in all these tests in dicates that albumin is not present. Physicians often make the serious error of adding too much nitric acid to thz urine at the start. This is dangerous, because if any considerable quan tity of nitric acid is added at the outset, it not infrequently happens that albumin will not be thrown down at all, even when much albumin is really present. The directions given above should, therefore, be followed implicitly, the urine being first boiled without any acid at all and then again after successive additions of a drop or two have been made, until as many as 15 or 20 drops have been added.
*Heller's test" tor albumin depends upon the fact that strong nitric acid throws down albu min from its solution, in the cold. In applying this test, a convenient quantity of strong, pure, colorless nitric acid is first placed in the bottom of a small test tube and an equal bulk of per fectly clear urine is allowed to flow down upon it gently, the test tube being inclined so that the urine may float upon the surface of the acid and not mix with it. If albumin is present, a sharp white zone appears at the surface of separation of the acid and the urine, the thick ness of this zone varying with the quantity of albumin. When normal urine is treated in this manner, a brown ring is formed at the surface of separation. In cases of fever, or when there is an excessive amount of coloring matter of any kind present, the albumin in Heller's test may be tinted, so as to appear brownish, red dish, violet or greenish. Urates, when present in excess, also give a zone marked by a pre cipitate; but the precipitated urates differ from albumin in being soluble when the urine is cautiously warmed without being allowed to mingle with the acid to any great extent.
In testing urine for the presence of sugar the test is ordinarily made to depend upon the fact that diabetic sugar will throw down a yel lowish or reddish precipitate of oxide of copper from an alkaline solution of copper sulphate and sodium (or potassium) tartrate. The test solutions that are ordinarily employed for this purpose are known, respectively, as (Tehling's solution* and gPavy's (qq.v.). In making a test, about one cubic centimeter of the test solution is placed in a test tube, diluted with about four times its own bulk of water and then boiled for a few seconds. If a pre cipitate is thrown down by this treatment, the test solution has spoiled and should be replaced by a freshly prepared one. If no precipitate is thrown down by boiling the test solution alone, the suspected urine should be immediately added, drop by drop. If any considerable quan tity of sugar is present, a precipitate will be obtained almost immediately. In the absence of a precipitate, however, the urine should be added, a few drops at a time, with occasional heating, until the quantity added is about equal to that of the original, diluted test fluid. If no precipitate is obtained, sugar, clinically speak ing, is absent. It should be observed that the formation of an actual precipitate must be ob served in this test; the mere decolorization of the blue test solution being no criterion of the presence of sugar. Other methods are known
for the detection and estimation of sugar in urine, but the copper test, as described above, is the one upon which physicians rely almost ex clusively.
The nitrogen waste of the body passes away mainly through the urine, in the form of urea, CON21-1,,. and of compounds of uric acid (C411•N401) with the alkalies and the alkaline earths. The approximate estimation of urea and uric acid is, therefore, often of considerable im portance. The determination of urea by the well-known *hypobromite process* is based upon the fact that sodium hypobromite, NaBrO, de composes urea quickly and completely in accord ance with the equation 3NaBrO'm 3NaBr CO2-1- 211,0 + 2N. The sodium bro mide (NaBr) that is formed remains in solu tion and the carbon dioxide (CO,) that is liber ated is absorbed by the test solution, which is made to contain a large excess of sodium hydrate. The only visible product of the de composition is the nitrogen gas, which is col lected and measured, and which serves to indi cate the quantity of urea decomposed. The hypobromite solution is made from water, caustic soda and bromine. Various proportions are used, but Tyson recommends dissolving 100 grams of caustic soda in 250 cubic centimeters of water and adding 25 cubic centimeters of bromine to the solution so formed. In practice the reaction is carried out in a special form of apparatus which has a vertical graduated tube to collect and measure the nitrogen. The ap paratus is first filled with the test solution and one cubic centimeter of urine is then introduced into it by means of a pipette. The decomposi tion of the urea begins at once, a copious ,stream of nitrogen bubbles passing up into the vertical collecting tube. In 20 minutes or less the reaction is complete and the number of cubic centimeters of free nitrogen is read from the graduated collection tube. For great re finement the volume of this gas must be cor rected to standard conditions of temperature and pressure; but for ordinary clinical purposes this is not necessary and it is sufficient to read the number of cubic centimeters of gas directly from the apparatus. Multiplying this number by 0.00282, we obtain the number of grams of urea that the given cubic centimeter of urine contained; and upon multiplying this product again by the total number of cubic centimeters passed by the patient, we obtain the total num ber of grams of urea passed. The total amount of urea passed by a healthy adult may range from 20 to 40 grams per 24 hours.
In health, practically all of the uric acid in the urine occurs in combination with potassium, ammonium, sodium, calcium and magnesium in the form of salts known as uurates.° Uric acid itself is highly insoluble, 14,000 parts of cold water dissolving only one part of the acid. To estimate the quantity that is present, 200 cubic centimeters of urine are acidulated by the addition of 20 cubic centimeters of nitric acid and set aside in a cellar or other cool place for 24 hours. The nitric acid gradually re places the uric acid in its combinations and the freed uric acid, owing to its insolubility, is de posited upon the sides and bottom of the beaker in the form of yellowish-red crystals. These may be collected, washed with cold distilled water and then dried and weighed; the weight so obtained giving the quantity of uric acid present in 200 cubic centimeters of the urine. In health, the quantity of uric acid passed by the kidneys in 24 hours may range from 0.4 to 0.8 gram. The heavy gbrick-dust" deposit that is often observed in urine that has stood for a time, and which is frequently referred to in the advertisements of proprietary ((kidney cures," for the purpose of terrifying the uninformed public into buying these consists mainly of urates, which are soluble at the temperature of the body but relatively insoluble at the ordinary temperature of a sleeping-room, and hence are likely to be thrown down. This sedi ment is found most commonly in urine that is somewhat more acid than usual. It also occurs in connection with defective assimilation of the food and is not to be regarded as of importance, unless it is markedly abundant or persistent; and even in these cases it points to an imperfect digestion rather than to trouble with the kidney. Consult Tyson, 'Practical Examination of .