340 PROTEIN-COMPOUNDS. 



reference being made to these difficulties. Scherer is the only 

 chemist who has directed attention to these obstacles in the way 

 of an exact determination of the albumen, and given instructions 

 regarding the manner in which they may be avoided. In order to 

 determine with exactness the quantity of albumen in a weak 

 alkaline fluid, we must neutralise or slightly acidulate it with 

 dilute acetic acid previously to coagulating it ; on the application 

 of heat, the albumen will then coagulate in flakes, and may be 

 both perfectly and rapidly collected on the filter, through which 

 the fluid will pass in a state of perfect clearness. By this method 

 another error incident to the ordinary mode of determining 

 albumen is avoided, for as we have already observed, some alkali 

 is always liberated on boiling any normal albuminous fluid, the 

 fluid exhibiting a stronger alkaline reaction than it did before the 

 boiling. This alkali forms, with a small quantity of albumen, 

 the so-called alkaline albuminate, which, notwithstanding the 

 boiling, remains perfectly dissolved. A portion of albumen 

 must therefore be lost in the ordinary method, even when the 

 coagulated albumen can be collected on a filter, for, as already 

 observed, some of the albumen actually passes through the filter 

 in a dissolved form. Scherer's method entirely obviates this cause 

 of error; care must, however, be taken not to run into an opposite 

 extreme in treating the albumen with too large a quantity of 

 acetic acid, which would equally occasion a loss of the albumen 

 by its solution in that fluid, and its consequent passage through 

 the filter. Hydrochlorate of ammonia may be employed instead 

 of acetic acid, but in this case a longer boiling is requisite, in 

 order completely to precipitate the albumen from the fluid, and to 

 render it capable of being collected on a filter. It depends entirely 

 on the other steps of the analysis whether acetic acid or carbonate 

 of ammonia be the best suited for the purpose. 



This is, perhaps, the most fitting place for drawing attention to 

 a point of the greatest importance in the quantitative analysis of 

 animal fluids, as well as of organic parts; we allude to the manner of 

 thoroughly drying substances to be weighed. The thorough drying 

 of animal substances which are in themselves hygroscopic, or which 

 contain admixtures of protein-compounds, extractive matters, &c., is 

 by no means so easy as that of already dry substances, which, in order 

 to be submitted to elementary analysis, have been exhibited in a per- 

 fectly pure state, and have been reduced to a pulverised con- 

 dition before weighing. It is obvious that dessication must be 

 effected with the same care as for an analysis with the combustion- 



