679 



liever he able to tix niiy shaip limits for the different ranges. Tlie 

 ordinary discriminalioii, liy gently sliaking or stirring, can only be 

 a rough one. We e.xamiiied if sharper criteria might be found by 

 means of the microscope, but it appeared, that the formation of little 

 lumps of a few or a great many small nibber-globiiles also took 

 place quite gradually, without sharp transitions, and that neitlier the 

 decrease nor the stopping of Brownian movement opened the way 

 for any sharp limitation. 



So most of our serial experiments were confined to judging at 

 sight, by means of a stirring rod, only completed occasionally by 

 microscopic oberservations. A short time, about 15 minutes, after 

 the addition of the acid the first observation was made, which 

 in certain ranges is already sufficient. The principal observation 

 followed two hours after the mixture was made, and was 

 controlled the next morning, viz. if then a stage was reached so 

 much fiiitlier advanced as might be expected from the condition, 

 such as it was two hours after the addition of the acid. In order 

 to be able to sufficiently overlook the whole, we have, in the 

 following paragraphs, interpreted the obsei'vations in a somewhat 

 simplified way ; therefore, with the cla.ssifications "stieaks", "curdled", 

 "porridge", and "coagulation" we have to associate the meaning of 

 conditions of sepaialion gradually passing into each othei', as described 

 above. 



As a rule we worked with 50 cc. of lit|uid for each determina- 

 tion, the liquid being left open to the air in a small cylindiic glass 

 till the next morning, for the last control-observation. With very 

 small quantities of acid the mixture of latex and water was meas- 

 ured with a measuring-cylinder and the acid was added liy means 

 of a burette. It was not necessary (o measure the diluted latex 

 more exactly than within ^ or 1 cc, but the acid had to be 

 measured exactly within one drop, especially with the very diluted 

 latices, where the range of coagulation is narrow and sharply 

 limited. With mixtures with larger quantities of acid, the latex, 

 eithei' diluted or not, was always mixed with the diluted or un- 

 diluted acid in such quantities that the total volume was 50 cc. ; 

 while the liquid, which occupied over half of the total volume, 

 was |:)oured out first, and the other one added to it. 



Especially in the range of a large (|uantity of acid, or if one 

 uses strong acid, it is necessary to stir \igoiously from the beginning, 

 so as to prevent local coagulation, which would cause enclosure of 

 acid, not being set free any more by further stirring. By making 

 one same final mixture, starting from latices of different dilutions 



