48 Chemical Manufacture. 



gas, but I am not aware that such an experiment has been 

 tried, or the results made public."* 

 January, 1845. 



Note on the above by Mr. A. Robertson. 

 * The description, referred to, of the apparatus for making sulphuric acid from 

 metallic sulphurets, seems to be complete without evasion or concealment, and 

 the apparatus itself to be admirably adapted for such a purpose. The theory of 

 the process given, is, however, faulty, and in the details there appears to be an 

 omission in regard to the saltpetre, which is not used alone, but mixed with its 

 equivalent of sulphuric acid. The nitric acid so evolved enables the sulphurous 

 acid gas to combine with oxygen, from the atmospheric air entering the lead cham- 

 ber along with it, in a manner explained in the well known theory of Clement 

 Desormes, which is noticed in every recent system or elements of Chemistry. 



From what Lieut. Latter states of the ore used, that it sometimes contains not 

 more than 1§ per cent, of copper, that there is much iron in the residuum, and that 

 it loses about one-fifth of its weight during the process, it is evident that much more 

 of the iron pyrites than of the copper pyrites must often be present in it. In this 

 case the process is a well known one, and has been carried on to a great extent 

 in Britain during the last five years at least, when it was forced upon the manufac- 

 turers by the attempted monopoly of Sicilian sulphur, which had tripled the price 

 of that article. 



It is merely a question of relative price whether pyrites or sulphur can be most 

 advantageously used. Sulphur, at present prices in Britain is likely the most 

 economical, even though the maker from pyrites be helped by the sale of the 

 residue to the iron smelters, as roasted iron ore. In Calcutta the sale of rough 

 sulphur (from Muscat) has been a monopoly in the hands of some native mer- 

 chants, and has ranged from two to three times the present price of rough Sicilian 

 sulphur in Britain, but it is said that abundance of very pure sulphur might be had 

 for the trouble of collecting it in many of the volcanic Islands in the Indian seas. 

 Acid made from volcanic sulphur is pure, that from pyrites usually contains much 

 arsenic, which unfits it for many purposes. 



There are at present three makers of sulphuric acid near Calcutta, who all sell 

 at the same price, two annas per lb. which considering the higher price of sulphur 

 in India, and the very limited sale of acid, is lower in proportion than that at which 

 it is sold in Britain, and it cannot well be expected to become less, while things 

 continue as they are, unless a party possessing capital should for some particular 

 reason be willing to submit to a temporary sacrifice. 



As connected with chemical manufactures in India, it may be well to notice that 

 a native production, sajee-mati, which a few years ago sold at less than one rupee 

 per maund, has, in Calcutta, for the last two years, advanced to from three to four 

 rupees per maund, and that British-made carbonate of soda has in consequence 

 been freely imported. It would be desirable to ascertain the reason of this, as it 

 is said to be abundant in some districts not far up the river, and to be had for the 

 labour of gathering it. The soda contained in the sajee-mati is probably as essential 

 to chemical manufacturers in India as sulphuric acid itself. 





