14(5 Scientific In I diligence. 



SCIENTIFIC INTELLIGENCE 



I. Chemistry and Physics. 



1. The Determination of Copjier as Sulphate. — Recoura 

 states that he has made a practice of weighing copper as anhy- 

 drous sulphate and finds the method extremely simple and accu- 

 rate, although it does not appear that the method has been 

 previously recommended. When a neutral solution of copper 

 sulphate is evaporated to dryness and the residue is heated in the 

 oven to 180-200° C, it loses the last traces of water with con- 

 siderable difficulty, and this fact is undoubtedly the reason why 

 the determination of copper in the form of the sulphate has not 

 been used. But Recoura has found that such is not the case 

 when a solution of copper sulphate containing free sulphuric acid 

 is thus evaporated and heated. Even when the amount of sul- 

 phuric acid is small, the salt when heated a short time at 180-200° 

 contains neither water nor sulphuric acid and reaches a constant 

 weight. The following results are given where exactly 1 g. of 

 copper sulphate was taken in each case : 



Time of heating 



Neutral solution 



Acid solution 



at 190° 



Eesidue 



Eesidue 



1 hour 



1-0045 



1-0005 



2 hours 



1-0040 



1-0001 



4 " 



1-0022 





48 " 



1-0006 





It appears, therefore, that the method is satisfactory, and that 

 it is to be preferable to the method of weighing cuprous sulphide, 

 at least in many cases. Many compounds of copper which con- 

 tain nothing that is not volatile at 200° may be treated with 

 dilute sulphuric acid in a platinum capsule, and then simply 

 evaporated, heated to 180-200° for two hours and weighed. 

 Other compounds of copper which are not directly soluble in 

 dilute sulphuric acid may be first dissolved in a little concen- 

 trated nitric acid, and then treated as before. The sulphide 

 requires roasting in a porcelain crucible over a good burner 

 before dissolving in nitric acid. — Bulletin, IV, vii, 832. 



H. L. W. 



2. A New Method for Determining Boiling Points and Vapor 

 Pressures. — Smith and Menzies of Chicago University have 

 devised an important method for making these determinations in 

 a very simple way with the use of very small quantities of sub- 

 stances. The substance is placed in a small glass bulb having a 

 capillary tube which is bent in a semi-circle just above the bulb, 

 so that its straight, open end is directed downward. The bulb 

 tube is then attached to a thermometer, and placed in a heated 

 liquid bath according to the usual manner of making melting- 



