Serolin is an azotised fat, which has hitherto only been found in the blood ; it is readily dis tinguished from cholesterin by its fusing point being much lower, 97° F., whereas cholesterin does not melt below 278°, and is found in the blood only in minute quantity. By pressing; them between folds of filtering paper we might therefore, if careful to maintain a temperature near that of boiling water, effect a tolerably complete separation of these bodies.
Butyrin rapidly absorbs oxygen from the air, setting free a volatile acid, the butyric ; it possesses the peculiar odour of rancid butter, by which its presence is always easily recog nized.
In analytical inquiries- it is best to separate fidty matters by ether as the first step after the liquid has been evaporated to dryness; we may then safely proceed to determine the Albumen.—In ,chemicat properties it differs little from fibrin, excepting in the fact of its requiring heat or some chemical agent to pro duce coagulation ; towards reagents it com ports itself in the same way. When liquid its separation from fibrin and fats is effecte as just described. The residue, after t fats have been removed by ether, is di gested in boiling Water, and the residue wc washed ; the albumen remains upon the filt and must be dried and weighed. A • quantity is incinerated to determine the portion of saline matters, which must ducted from the weight previously found uric acid existed in the solution, it wo mixed with the albumen. In me the c ing matter of the blood were contained • fluid, a small part would remain mixed the albumen, and might be removed gestion in alcohol acidulated with sul acid, by which the hmmatosin is dissolved greater part, however, subsides by all the liquid to stand undisturbed in a tall for forty-eight hours. If the solution c free alkali, a part of the albumen is redis on the addition of water; when, therefor filtered liquisl presents an alkaline reactt should be very carefully and exactly neut by acetic acid, evaporated to dryness, and treated with hot water; the weight of this portion of albumen must be added to dr obtained. Casein hardly ever occurs i same solution with albumen ; if pros would be separated by the acetic acid manner already described.
Casein is distinguished from albumen non-coagulability by heat ; when its sol are evaporated at a high temperature, an luble skin or film forms upon die su which is almost characteristic, the only with which it can be confounded being an alka line solution of albumen, which resembles it in this and in some other particulars. Acetic
acid in small excess causes its immediate coagulation ; a great excess of the acid redis solves the coagulum. The fibrin, fats, and albumen having been separated in the manner already descrihed, we may proceed to deter Mine the casein by adding a few drops of acetic acid and evaporating to dryness. Boiling water removes from the residue every thing ex cept saline matters and casein ; this residue is dried, weighed, incinerated, and the salts de ducted; a portion of casein is apt to redissolve in the water, so that this process is not perfectly accurate.* Urea.—lt is best, when practicable, to make a separate analysis for this principle; if this be impossible, we may proceed with the fluid from which albalmen, casein, and fats have been.se parated, as already mentioned. In either case the liquid is evaporated to dryness, and the re siduum digested with alcohol; we thus obtain a solution of urea freed from every thing ex cept chlorides, sugar, some " extractive" mat ters, besides fats and lactates, unless previously removed by ether. The alcohol having been driven off, the residue is dissolved in sufficient water to produce a liquid of syrupy consistence. Colourless nitric acid is diluted till of a specific gravity of 1.25, which is a convenient strength for precipitating the nitrate of urea. The eva porating basin with the impure solution of urea is next placed in a vessel containing a frigorific mixture composed of 1 oz. of nitre, 1 of sal ammoniac, each finely powdered, and 4 oz. of water ; when the basin and its contents have been thus cooled, colourless nitric acid, sp. gr. 1-25, rather more than equal in bulk to the solution of urea is added drop by drop, stir ring carefully; Wadded too quickly, the tempe rature rises, a little effervescence ensues, and part of the urea is decomposed. A flaky precipi tate shows nitrate of urea ; the vhole is al lowed to remain in the freezing mixture for hree or four hours, or even longer; the nitrate f urea is then collected on linen, the linen is olded up, placed between several layers of Itering paper, and then subjected to strong essure. The mother-liquor and excess of cid are thus almost entirely expelled ; a slightly iscoloured firm dry mass of nitrate of urea is °cured, which may be exposed for some time a temperature of 2129, and then weighed ; 00 parts contain 48.78 of urea. The amount f impurity which this nitrate contains is usu lly very small, as is easily proved by ultimate talysis.