Intelligence and Miscellaneous Articles. 317 



one pound of water at 39°- 1 Fahr., its temperature of greatest den- 

 sity ; whereas it is possible that, in the statement of the experimental 

 results, the volume of the steam may have been compared with that 

 of water at a higher temperature. 



Ratio of volume of steam to volume of water. 

 Temperature Fahr. gy theory. By experiment. Difference. 



244 936 896 +40 



245 920 890 30 



257 756 751 5 



262 698 684 14 



268 635 633 2 



270 616 604 12 



283 506 490 16 



I am. Gentlemen, 



Your most obedient Servant, 

 Glasgow, September 24, 1859. W. J. Macquorn Rankine, 



ARSENIC IN PYRITES. 



To the Editors of the Philosophical Magazine and Journal. 



Gentlemen, 



In the August Number of your valuable periodical, I see an 

 article by Professor Davy " On the Presence of Arsenic in some 

 Artificial Manures, and its absorption by Plants grown with such 

 Manures," which has an important bearing on the question of sul- 

 phur V. pyrites in the manufacture of sulphuric acid, to the prejudice 

 of the latter, too conclusively, as I will endeavour to show. 



There is nothing new in the statement that plants are capable of 

 absorbing arsenic from artificial manures, nor that the sulphuric acid 

 used in their preparation when made from pyrites commonly con- 

 tains arsenic ; and hence it is common in the chemical market for 

 buyers of superphosphate to stipulate that it shall be made with 

 vitriol prepared from sulphur. 



All pyrites, however, does not contain arsenic. Until the price of 

 sul})hur was so much advanced, which has enormously increased the 

 demand for pyrites, the manufacturers of vitriol depended upon the 

 United Kingdom for their supplies, and Cornwall and Wicklow fur- 

 nished the chief portion, in which arsenic was invariably met with. 

 Large importations have, however, arrived from foreign countries of 

 a different character, and some of them contain no arsenic at all. 

 In particular that which has come from Belgium, exported by the 

 " Belgian Pyrites Company of Antwerp," has been repeatedly tested 

 for arsenic by different operative chemists, without ever showing a 

 trace ; it is nodular, with crystalline fracture, and very rich in sul- 

 phur, generally testing from 48 to 50 per cent. Spain has also fur- 



