The colourless solution was filtered, dried, and then treated with alcohol of specific gravity .845. Equal parts of strong sulphuric acid and water were now added, guttatim, to the alcoholic solution, until sulphate of lime no longer precipitated ; the clear liquor being decanted was next treated with carbonate of lead (recently precipitated), and was then filtered and evaporated to dryness.
The residue was treated with oxide of lead and a little water, by which means the lactic acid was converted into a sub-salt of consider able insolubility. This was collected, washed with water, and then decomposed by sul phuretted hydrogen. Thus, sulphuret of lead subsided, leaving the lactic acid free in the supernatant liquor, which, by evaporation, yielded it in the form of an acid yellow syrup, exceedingly deliquescent, and incapable of being thoroughly dried by heat.
Its chemical properties are the following : It gives out an acrid odour * when heated, and leaves a porous charcoal if the heat be continued. Alcohol dissolves it in all propor tions. It is nearly insoluble in ether.
Its salts are all of a gummy and uncrystal lisable nature, excepting the lactates of zinc and magnesia, which have been obtained in a crystalline form.
When lactic acid is added to a strong solu tion of the acetates of magnesia or oxide of zinc, the lactates of those bases are pre cipitated.
The existence of lactic acid, as a consti tuent of urine, has been denied by Liebig, and the question is as yet far from being satisfac torily settled.
The admission made of late by Liebig, how ever (as the result of his researches on muscle), that lactic acid exists in the juice of flesh, gives great probability to the correctness of Berzelius's statement.
The other constituents of the urine which 1 have enumerated, require no particular notice in this place ; and for the methods of quantitatively examining the fluid, I must refer to the article ORGANIC ANALYSIS, contained in this work.
Healthy urine possesses the following phy sical characters : — It is of a pale straw colour, limpid and acid ; after standing some hours, it deposits a light, flocculent sediment, com posed of mucus. This mucus, as it exists in health, suspended in the urine, does not materially interfere with the transparency of the fluid. The odour of urine is peculiar, and
subject to modification from the use of various articles of diet, and remedies. Its specific gravity varies, owing principally to two causes — the condition of the atmosphere, as affect ing the proportion of water exhaled by the skin, and the quantity and quality of the in gesta taken.
Healthy urine may, under these considera tions, be said to vary in specific gravity from 1001 to 1032 ; while perhaps, under ordinary or average conditions of diet, temperature, &c., we may place its specific gravity at 1015 to 1022.
Quantitative composition of healthy Urine.— The quantitative composition of urine must of course vary considerably, owing to the condi tions noticed above, as affecting its specific gravity. The following is the result of an analysis made on 1000 parts by Berzelius, on a specimen considered as healthy:— Dr. Bence Jones has experimented very carefully on the acidity of urine in health. His results show that the amount of acidity is always varying. Thus the urine passed longest after food was generally the most acid, and that voided while digestion was going on, much less so, and in some cases even alkaline, though the patient was in perfect health. These conditions pertained, whether a pure vegetable or animal diet was taken. In the case of a pure vegetable diet, however, the decrease in acidity, after taking food, was not so marked as when a pure animal diet was observed ; the urine in the latter case some times becoming highly alkaline, but in the former never exceeding neutrality.
Other analyses of more recent date have been published by the following observers, viz. Marchand, Simon, Becquerel, Leh mann, &c. I shall quote several of these from the work of Franz Simon, which has been excellently translated into English by Dr. Day, for the Sydenham Society.
Simon analysed two specimens of the urine of a healthy man, 33 years of age. He was of sanguineous temperament. The specific gravity was in the first case 1011, and in the second 1012.
1000 parts yielded — The specific gravities of the urines which yielded these above analyses, judging from the amount of solid content, must have been as high as from 1022 to 1029. This is very high, indeed, as an average of 24 hours.