220 REPORTS OX THE STATE OF SCIENCE. 



tiiue lilt; total acid iu the jelly is diuiiiiisliutl, but tlic ' lixcd acid ' la 

 gradually, though nob largely, increased. It is probable that if the con- 

 centration of the hydrochloric acid could be increased to an equal extent 

 to that of the salt without causing solution an equal dehydration would 

 be produced, and it is difficult to resist the conclusion that the swelling 

 is due to the chlorine ion iu the acid gelatine, and is osmotically 

 repressed by the increase of the same ion in the solution. Other acids 

 with their neutral salts produce similar effects. The fact that similar 

 dehydration is produced by other acids, e.r/., sulphuric, in conjunction with 

 sodium chloride, and probably with other salts, does not contradict the 

 conclusion that it is the common anion which is operative, since in the 

 case suggested an equilibrium of sodium and gelatine sulphates and sodium 

 and gelatine chlorides would result. The cause of the general swelling 

 effect of acids must, however, in some way be intimately connected with 

 their common H ion, and that of alkalies, which is equally powerful, 

 with the hydroxyl ion. The alkaline swelling is not repressed by sodium 

 chloride, even when caused by sodium hydrate, but is repressed by 

 sufficient concentration of the hydroxyl ion in the outer solution. The 

 above are the summarised results of a research on which the writer has 

 been some time engaged, and which he hopes shortly to publish with a 

 more detailed discussion of the operating causes. It may be remarked 

 that the dehydration of ;icidiHed gelatinous tissues has an important 

 technical application in the preservation of sheep pelts by ' pickling ' 

 with salt and suljahuric acid, and its bearing on mineral tannages in 

 which salt is employed with alums and other compounds of acid reaction 

 is very obvious. As gelatine is decidedly amphoteric, and is known 

 to be capable of decomposing many salts in solution, it is quite pos- 

 sible that some of the complicated effects of unacidified salt solutions 

 which have been referred to may be due to partial absorption of the 

 acid of the salt and the osmotic effect of the remainder on the compound 

 formed. 



.Space will not allow of any detailed discussion of the coagulation of 

 the various albumins by heat and precipitating agents, which, important 

 as they are from the physiological aspect, have not yet yielded many facts 

 which can lie explained on general principles. Albumins, carefully freed 

 from electrolytes by dialysis, are electrically neutral and incompletely 

 coagulated by heat or by those precipitants which do not at the same time 

 communicate an electrical charge. The addition of a trace of acid which 

 gives a positive charge renders them liable to complete coagulation by 

 heat and much more sensitive to the action of electrolytes ; but larger 

 ([uan titles of acid, perhaps by producing soluble acid albumins, prevent 

 coagulation. Traces of alkalies which give a negative charge have a 

 similar effect, though the precipitation is usually less complete, and excess 

 again prevents or lessens precipitation. Coagulation by heat is usually 

 irreversible, and so also that by alcohol, though zymases are precipitated 

 by the latter in a reversible (soluble) form. Salts of the heavy metals, 

 even in small quantities, produce irreversible coagulation, very possibly 

 connected with combination, or colloidal precipitation with a colloidal 

 compound of the metal. Excess of the precipitant frequently prevents 

 precipitation, probably by the formation of new complex compounds. 

 Possibly there may be some connection between these phenomena and 

 the irreversible (tanning) effects of some metallic solutions on gelatinous 

 tissues. These solutions are usually of 'basic salts ' containing metallic 



