[91] COLLECTING AND PEESERVING INSECTS RILEY. 



that pure rubber- stoppers used for cliemical j^urposes would not pre- 

 sent tbis disadvantage, wbicb maybe obviated, however, or very much 

 reduced, if the stoppers are washed or soaked, preferably in hot water, 

 for an hour or two at least. 



If stoppers are stored for a considerable time and exposed to the air 

 they become very hard and unfit for use, and Dr. Hagen has dra,wn at- 

 tention to a method recommended by Professsor W. Hemple, of Dres- 

 den, Saxony, of preventing them from becoming thus hardened. He 

 says that to keep rubber stoppers or rubber apparatus of any sort 

 elastic, they should be stored in large glass jars in which an open vessel 

 containing x)etroleum is placed. This treatment prevents the evapora- 

 tion of the fluids which are fixed in the rubber in the process of vulcan- 

 ization. It is better also to keep the light from the jar. To soften 

 stoppers which have already become hardened, they should be brought 

 together in ajar vnth. sulphuret of carbon until they are pliable and 

 afterward kept as recommended above. 



In the use of the rubber stoi^per the novice may find some difftculty 

 in inserting it in a vial filled with alcohol. The compression of the alco- 

 hol, or alcohol and air when the vial is not completely filled, forces the 

 stopper out, and this is true whether of rubber or cork. If a fine insect 

 pin is placed beside the cork when this is thrust into the bottle, the air 

 or liquid displaced by the cork will escape along the pin and the latter 

 may then be removed and the cork remains securely in position. 



If cork stoppers have been used the vials may be stored in large 

 quantities together in jars filled with alcohol. This will prevent evap- 

 oration of the alcohol from the vials, and the specimens may be pre- 

 served indefinitely. This is only desirable in the storage of duplicate 

 specimens and unarranged material and is not recommended as a sub- 

 stitute for the use of the rubber stopper. With cork stoppers evapor- 

 ation can be in a measure prevented if the cork is first anointed with 

 the petroleum preparation known as vaseline. This substance is prac- 

 tically unaffected at ordinary temperature and is sparingly soluble in 

 cold alcohol. Experiments with it have shown that at ordinary spring 

 and summer temperatures there is no appreciable loss of alcohol from 

 vials and jars. 



My old method of keeping alcoholic specimens, which I abandoned 

 for the method outlined above, was fairly serviceable, inexpensive, and 

 warrants description. 



I had special folding boxes constructed resembling in exterior ap- 

 pearance a large insect box. The bottom of the box was sohd and was 

 made by gluing together two 1^-inch planks. 



Holes extending nearly through the lower plank and of various sizes 

 to accommodate vials of different diameters were bored as closely to- 

 ^'ether as the wood justified without splitting or breaking. 



The holes were numbered consecutively and the vials when placed in 

 them were numbered to correspond j the box also had its number, and 



