504 , NEW YORK STATE MUSEUM 



not unlike kaolinite in its behavior, as shown bj the experiments 

 of Vogt, its presence may be of no influence, unless there is an 

 appreciable amount of it. The following quotation-^ exhibits those 

 experiments. 



Mr Vogt considers that the plasticity which clays have is chiefly 

 due to the hydrated silicate of alumina or kaolinite. Experiments 

 which he made, show that the kaolinite is not the only substance 

 which remains in suspension for a long period. For his trials he 

 took quartz from Limousin, orthoclase from Norway, and a potash 

 mica. AH three were ground very fine, and then washed in a 

 current of slightly ammoniacal water. The washed materials were 

 then allowed to stand. After 24 hours each of the liquids was 

 as opalescent as if it had washed clay in suspension. After nine 

 days the turbidity still remained, but was less marked. At the end 

 of this time the supernatant liquid was ladled off of each, and a 

 few drops of hydrochloric acid added to it. The suspended ma- 

 terials coagulated and settled, and the precipitate was collected, 

 dried, and weighed. The mica which had remained in suspension 

 during the nine days was very fine; still the particles glittered in 

 the light. The addition of hydrochloric acid caused the instant 

 settling of the particles, which was also noted by the cessation of 

 the glittering. The settlings of mica from 1 liter of water 

 amounted to .15 gram. This fine-grained mica possessed a plas- 

 ticity almost equal tO' that of the kaolin. 



From the decanted liquid of the feldspar the hydrochloric acid 

 brought down .4 gram of this mineral per liter, while of the 

 quartz only .1 gram of sediment was obtained. 



A very plastic clay from Dreux was treated in the same manner 

 and after nine days a precipitate of .56 gram was brought down. 



From these experiments we see that in washing kaolin it is 

 impossible to free it entirely from quartz, feldspar, and mica. 



Associated with kaolinite we may find one or more other specie? 

 of minerals, all hydrated silicates of alumina. Some of these have 

 been found in crystals and are very probably good species, but 

 others are known only in an amorphous condition. This may tend 

 to suggest some doubt as to their validity. These associated species 

 together with their characters are given by Dana as follows. 



^ Thonindustrie zeitung, 1893. p. 140. 



