THE CANADIAN ENTOMOLOGIST. 



much better. After all, I think the result is a decided success. All the 

 so-called pure rubber stoppers for chemical laboratories of American 

 make are, as far as I am able to ascertain, manufactured of vulcanized 

 rubber, which is not the case with those imported from Germany. The 

 Professor of the chemical laboratory here has had the same experience. 

 The 7,800 stoppers of different sizes have cost about $110 ; if they had 

 been bought at once at wholesale figures, the price would have been 30 

 to 35 per cent. less. 



As the stock in hand for the advancement of the collection has to be 

 a large one, I may draw attention to a method recommended by Prof. W. 

 Hempel, of Dresden, Saxony, to prevent the stoppers becoming too hard 

 (Bericht d. Deutsch. Chem. Gesell., 1882, vol. xv., Heft. 6, No. 184). 

 Rubber stoppers or tubes retaining their elasticity should be kept in large 

 glass jars, in which an open vessel with petroleum has been placed. It is 

 better to keep the light from the jar ; wooden boxes should not be used. 

 Stoppers which have become hard should be brought together in a jar 

 with sulphuret of carbon until they are softened, and afterwards be kept 

 in a jar with petroleum just as the others. Before knowing this I used to 

 soften such stoppers by squeezing in different directions, or by rolling with 

 a piece of board. Of course Prof Hempel's method is better, as it pre- 

 vents the gradual evaporation of the fluids used for the solution of the 

 rubber in the process of vulcanization. It is remarkable that until now 

 none of the stoppers in the vials arranged in wooden boxes have become 

 hardened, though the same stoppers not fixed in vials with alcohol grew 

 hard. Probably the strong pressure of the alcohol by fitting the stoppers 

 has some influence in keeping them soft ; besides, the part of the stopper 

 outside of the vial is mostly small. I do not know whether rubber stop- 

 pers for similar purposes have been used here or in Europe earlier than in 

 the Cambridge Museum ; if so, I would be very glad to know the results 

 obtained elsewhere. 



PRELIMINARY LIST OF THE SPECIES OF ACARINA OF 



NORTH AMERICA. 



BY HERBERT OSBORN, OF THE IOWA AGRICULTURAL COLLEGE, AND 

 LUCIEN M. UNDERWOOD, OK SYRACUSE UNIVERSITY. 



I'he Acarina, especially the more minute forms, have been but little 

 studied in America, a fact which seems the more strange when we con.' 



