1890.] NEW-YORK MICROSCOPICAL SOCIETY. 89 



during all the following processes. This prevents all rolling or 

 folding, as well as the shrivelling of the film, when coming suc- 

 cessively in contact with liquids of different specific gravity and 

 of different chemical qualities. To smooth a folded or rolled 

 film is sometimes very tedious, but to remove wrinkles, caused 

 by shrivelling, is impossible. 



Whenever the film of gum-arabic comes in contact with water, 

 it is dissolved, and the paper support and the film of collodion 

 are separated. This premature separation can be prevented in 

 different ways. One way is to leave outside of the space 

 intended for the sections a margin free from mucilage. If the 

 solution of collodion is brushed over this ungummed paper, the 

 collodion will soak the paper and stick fast to it. Another way 

 is to fasten and cover the sections in the manner described, but, 

 before the immersion in turpentine, a dented wheel, such as is 

 used for tracing patterns, is run along a line outside of the space 

 containing the sections. Through the holes thus made the col- 

 lodion comes in contact with the paper below the gummed sur- 

 face and sticks to it. As soon as the treatment is finished, col- 

 lodion-film and paper-support can easily be separated from each 

 other, in either of the described methods, by cutting away the 

 lines of margin where collodion and paper stick together. 



b. The hardening of the collodion in the bath of turpentine 

 takes place on removing the alcohol, ether and castor-oil, these 

 being dissolved by the turpentine. For the purpose of doing 

 this, as thoroughly as possible, a second bath of fresh turpentine 

 is to be used. If work is continued, the liquid of the second 

 bath can be used later as the first one. Warming the baths 

 slightly will shorten the time required for the removal of the 

 films from the liquids. 



c. First, the surplus of turpentine is now allowed to drain off, 

 then the support with the film is put between thick layers of 

 filtering paper. This is repeatedly renewed, and the whole is 

 subjected to a constant pressure for some time. The sections 

 are not likely to be damaged by this pressure, if the collodion- 

 film is not too thick, and has before been sufficiently hardened. 

 Now a bath of equal parts by weight of chloroform and 95 per 

 cent, alcohol is employed from one-quarter to one-half of an 

 hour, to remove the last traces of turpentine. If then transferred 



