4 ANIMAL JUICES. 



check ; but it would be superfluous to indicate any special methods 

 of control, since every analysis of an animal fluid, and even almost 

 every individual determination, admits of being tested by the most 

 rigid purely chemical checks. We shall find that these controlling 

 or controlled analyses frequently afford the most unexpected proofs 

 of the value of the method of analysis, by the light they throw 

 upon the true constitution of the object under examination. 



C. Schmidt* has employed an ingenious and original method 

 for ascertaining the correctness of the complete analysis of an 

 animal fluid; it consists in comparing the empirically found 

 specific weight, with the sum of the specific weights of the indi- 

 vidual constituent parts, according to the proportions yielded 

 by the analysis. Such a controlling calculation of the density 

 cannot of course be based upon the specific weights of the dried 

 substances and of the water ; since all substances when dissolved 

 in water undergo a condensation with it. It is a highly important 

 circumstance in relation to the complete physiological considera- 

 tion of the animal fluids and of the mechanical metamorphosis of 

 matter, that the dissolved substances do not occur, as has been 

 generally supposed, in a mere condition of mechanical distribution 

 and admixture, but that when dissolved in different quantities of 

 water, they enter into different hydrate-like combinations with 

 that fluid, and consequently exhibit various degrees of condensa- 

 tion. Schmidt has determined the coefficients of condensation 

 for the ordinary constituents of animal fluids, and made the 

 density of the solutions which contain exactly 10 of solid sub- 

 stances (at + 15 C. in vacuo) the basis of his controlling check. 

 Knowing the relations of the individual constituents from the 

 analysis, we may easily calculate the specific gravity of the collec- 

 tive fluid from the sum of the coefficients of condensation, and 

 may then compare it with the empirically found specific gravity. 



The following illustration will serve to elucidate the table 

 compiled by Schmidt for the purpose already stated. The specific 

 gravity of chloride of sodium (at + 15 C. in vacuo) is = 2'1481 ; 

 hence, if the salt in a solution containing lOf of chloride of 

 sodium were distributed in the water without condensation, this 

 solution would have a specific gravity of 1/0565 ; for 10 parts of 

 dry chloride of sodium (its specific gravity being = 2*1481) occupy 

 the space of 4'655 parts of water ; with 90 parts of water, there- 

 fore, the solution should occupy the space of 94'655 parts of 



* Characteristik der Cholera. Mitau, 1850, S. 22 28. 



