680 



and differently strong arids, one may liowever control llie observa- 

 tions in a satisfactory way. 



On account of tiie increasing acidity of tlie latex itself it is not 

 advisable to use it more tlian about two hours before the observa- 

 tions; we only did determinations between 10 a.m. and noon, but 

 during that time one can easily prepare a few series, in total about 

 tliirty to fifty mixtures, so that in a rather short time l)y many 

 hundreds of observations one can search the whole range of mixing 

 in all directions. 



Operating in small, open cylindrical glasses, causes a certain 

 evaporation and lesults in the formation of a small superficial skin 

 of coagulated rubber, which on stirring attaches itself to the 

 stirring-rod. 



Apparently this causes an undesired complication; but for distin- 

 guishing different liquid mixtures this formation of skin appeared 

 on the other hand an advantage, because it enables us to recognize 

 the liquids inclined to coagulate. By repeating a few series in small 

 Erienmeyer-flasks, closed with a cork, we have ascertained that 

 really these skins are formed by evaporation at the surface. 



^ 3. Hydrochloric acid. 



The easiest way to summarise the phenomena at different dilutions 

 and different quantities of acid, is to draw these in the wellknown 

 triangle-figure. As angular points fcom|)onents) we choose water, 

 concentrated hydrochloric acid (9.14 N) and undilated latex, i.e. a 

 liquid with 31.8 % coagnlable rubber, about 35 "/, totally solid 

 substances and about 65 "/o water, and with an acidity of about 

 0.03 N. A recalculation of the results, so as to express these as 

 quantity of acid, resp. rubber compared to the whole liquid (water 

 of dilution plus serum) can never be correct by the phenomena of 

 adsorption and, as regards rubber, there is not much sense in it, 

 as coagulable rubber is a substance containing so many secondary 

 substances in small quantities. 



In the annexed figure 1 the lines show how the different mixtures 

 are formed by mingling latex and hydrochloric acid, of different 

 dilutions. The mixtures, in which after two hours a well coherent 

 coagulum was formed, are marked with a little cross. As we see 

 this range almost occupies the whole triangle; only in a narrow 

 strip along the latex-water side, we find mixtures, which are 

 represented by an encircled point (pap or curdling) or by a little 

 circle (liquid), and there we can, though indistinctly on account of 



