THE ALUMNI JOURNAL 165 



tion and place and kept under the same restrictions regarding tem- 

 perature, light, etc., will show a marked variation in keeping. The 

 contents of one bottle will lose scarcely no strength, while another 

 will deteriorate rapidly. The reason for this is hard to explain unless 

 we attribute it to the action of the cork or possibly some particles of 

 foreign matter left in the bottle after washing. This argument can 

 hardly be sustained, however, as experiments show that the same 

 phenomena takes place with peroxide stored in glass stoppered bottles 

 previously washed with distilled water and alcohol and afterwards 

 sterilized. It is possible that a variation in the composition of glass 

 may have some decomposing influence. 



CONCENTRATION OF PEROXIDE. 



The ordinary 3 per cent, solution may be concentrated in varuum 

 to as much as 100 per cent. It may be made to about 15 per cent. 

 by carefully concentrating oh an open water bath, using as little heat 

 as possible. This practice is frequently resorted to by dentists in 

 their practice, where a powerful bleaching or cleansing action is 

 desired extemporaneously. 



Staedel has produced peroxide in pure crystalline form of 100 per 

 cent, purity, by solidifying a concentrated aqueous solution 95 per cent, 

 in strength in an ether carbonic freezing mixture. Explosive decom- 

 position of the crystals took place immediately in contact with foreign 

 matter. A 3 per cent, solution of peroxide may be concentrated to 

 as much as 50 per cent, in strength by cautiously exaporating on 

 water bath at a temperature of not over 60 degrees C. The solution 

 becomes stronger by the evaporation of water as the water is driven 

 off much faster than the oxygen can be liberated. 



( To be Continued.) 



Ichthyol Tests. — In the "Chemist and Druggist," Dec. 18, 1909. 

 Dr. F. \Y. Passmore, writing in regard to organic sulphur prepara- 

 tions of the ichthyol type, stated that the combined sulphur is the 

 most important constituent in these preparations, and he gave 

 analytical figures which show that ichthyol is distinguished from its 

 substitutes by containing 12.5 per cent, of "sulphidic" sulphur in the 

 organic dry residue, and 6.1 per cent, of sulphonic sulphur, while 

 the composition as a whole is remarkably constant. His conclusions 

 have been confirmed generally by Dr. Aufrecht ("Allgem. Mediz. 

 Central-Zeit.," 1912, 69), who gives analyses of ichthyol and ichthy- 



