372 Mr. H. A. Smith on some Points in the 



Deposit in flue leading from kilns to lead chamher. — This flue 

 when cleaned out presented a strange appearance. Its length 

 was about 20 feet^ and, with the exception of about 10 feet from 

 the "kiln^^ end, was thickly coated (and even partially filled) with 

 a shining deposit, which on examination proved to be a mass of 

 sulphur in a perfectly viscous state^ containing (as a mean of four 

 analyses) 46'360 per cent, arsenic trioxide. 



When lighted it burned with the ordinary blue sulphur-flame, 

 and on inserting a piece of cold porcelain in the vapour, gave a 

 deposit of sulphur along with a considerable amount of arsenious 

 acid. (See Table II.) 



Sulphuric Acid. — Passing along the flue into the chamber, I 

 find the sulphuric acid containing a large amount of arsenic. As 

 an average of twelve analyses, J '051 per cent, arsenious trioxide 

 is the result ; so that in passing through the flue above men- 

 tioned it must have lost a large proportion of that originally pre- 

 sent in the pyrites. (See Table II.) It is from the sulphuric 

 acid itself that the arsenic should be removed, as this acid is the 

 groundwork of the whole following alkali-manufacture. 



Deposit on bottom of lead chamber. ^On the bottom of the lead 

 chamber and sometimes on the sides, a grey siliceous mass is 

 found, interspersed here and there with clusters of delicate regular 

 crystals, the transparent elongated prisms of arsenic acid. The 

 transformation from the arsenious acid we find in the flue to the 

 arsenic acid of these crystals, has evidently been completed along 

 with the oxidation of the sulphurous acid. In this deposit the 

 percentage of arsenic trioxide varied from 1*811 to 1-9 per cent., 

 the rest consisting of sulphate of lead and silica. (See Table II.) 



Hydrochloric Acid. — ^AYhen the sulphuric acid made from py- 

 rites is mixed wnth common salt in the reverberatory furnace for 

 the formation of sodium sulphate, the arsenious acid present in 

 the acid is converted into the terchloride of arsenic, and escapes 

 along with the hydrochloric acid to the condensing-towers. This 

 conversion is very nearly complete, as the amount of arsenic pre- 

 sent in the sodium sulphate is very small. In the hydrochloric 

 acid a mean of eight analyses gives 069 per cent, arsenic trioxide, 

 the amounts varying from 0-589 to 0-911 per cent. (See Tablell.) 



Sulphate of Soda. — The amount present in this is very small. 

 As mentioned above, the conversion from the teroxideto the ter- 

 chloride of arsenic is wonderfully complete, the percentage in the 

 sodium sulphate being only 0*029 per cent. (See Table II.) 



This still shows us how careful we ought to be in obtaining 

 pure sulphate of soda for medicinal purposes. 



Deposit in flue leading from salt-cake furnace to condensing- 

 toivers. — This flue, about 20 feet long, leads for the most part in 

 the open air, from the salt-cake furnace to the condensing-towers. 



