Robert's test is one of the best for routine work, although the various rings are apt to be confusing to the inexperienced. It is more sensitive than Heller's test, of which it is a modification, and has the additional advantage that the reagent is not so corrosive.
(3) Purdy's Heat Test.—Take a test-tube two-thirds full of urine, add about one-sixth its volume of saturated solution of sodium chlorid and 5 to 10 drops of 50 per cent. acetic acid. Mix, and boil the upper inch. A white cloud in the heated portion shows the presence of albumin.
| FIG. 23.—Esbach's albuminometer, improved form. |
This is a valuable test for routine work. It is simple, sufficiently accurate for clinical purposes, and has practically no fallacies. Addition of the salt solution, by raising the specific gravity, prevents precipitation of mucin. Albumose may produce a white cloud which disappears upon boiling and reappears upon cooling.
(4) Heat and Nitric Acid Test.—This is one of the oldest of the albumin tests, and, if properly carried out, one of the best. Boil a small quantity of filtered urine in a test-tube and add about one-twentieth its volume of concentrated nitric acid. A white cloud or flocculent precipitate (which usually appears during the boiling, but if the quantity be very small only after addition of the acid) denotes the presence of albumin. A similar white precipitate, which disappears upon addition of the acid, is due to earthy phosphates. The acid should not be added before boiling, and the proper amount should always be used; otherwise, part of the albumin may fail to be precipitated or may be redissolved.
Quantitative Estimation.—The gravimetric, which is the most reliable method, is too elaborate for clinical work. Both Esbach's, which is very widely used, and the centrifugal method give fair results.
(1) Esbach's Method.—The urine must be clear, of acid reaction, and not concentrated. Always filter before testing, and, if necessary, add acetic acid and dilute with water. Esbach's tube (Fig. 23) is essentially a test-tube with a mark U near the middle, a mark R near the top, and graduations ½, 1, 2, 3, etc., near the bottom. Fill the tube to the mark U with urine and to the mark R with the reagent. Close with a rubber stopper, invert slowly several times, and set aside in a cool place. At the end of twenty-four hours read off the height of the precipitate. This gives the amount of albumin in grams per liter, and must be divided by 10 to obtain the percentage.
Esbach's reagent consists of picric acid, 1 gm., citric acid, 2 gm., and distilled water, to make 100 c.c.
(2) Purdy's Centrifugal Method.—This is detailed in the accompanying table. The percentage by weight is approximately one-fiftieth of the bulk percentage.