Chemistry of Acid-manufacture. 



Z11 



Table VII. 



Specimens of Air taken 10 feet from the bottom of Chimney. 

 Amount of air taken for each analysis = 500 cubic feet. 



No. of analysis. 



As"^ 03 per 1000 cubic 

 feet. 



2.* 

 3. 

 4. 

 5. 

 6. 

 7. 

 8. 

 9. 



grain. 

 0046 

 0-022 

 0086 

 0062 

 0112 

 0054 

 0122 

 132 

 0144 



0780 





0-086 



I hope to speak in another part of this paper on some of the 

 methods employed for the removal of this " nuisance ; '' in the 

 mean time I must proceed to speak of the remaining substances 

 of alkali- manufacture. The last examined was the sodium sul- 

 phate ; the next to undergo analysis was the 



Sodium Carbonate. — This, up to the present time, has been 

 found perfectly free from arsenical impurity; fifteen samples 

 from twelve different works were submitted to analysis, and none 

 was discovered. 



Soda-waste, — In this the amount is comparatively trifling, 

 giving as an average of six analyses 0*442 arsenic trioxide. (See 

 Table II.) 



Recovered Sulphur. Mond's process, before and after purification. 

 — In specimens of sulphur recovered by Mond^s process I have 

 sometimes found great differences, the amounts varying some- 

 times from 0*442 to 0*901 per cent, arsenic trioxide ; but its 

 presence to this extent is only found in the unpurified samples. 

 In those which have undergone purification none whatever is 

 found, the average of four analyses of the unpurified sulphur 

 being 0*7 per cent. 



I think the foregoing analyses allow a simple and direct de- 

 duction to be drawn ; and that is, if the arsenic is to be removed 

 at all, every thing points to the sulphuric-acid stage as that in 

 which the removal ought to take place. Sulphuric acid is the 

 corner-stone of alkali-manufacture ; cleanse it, and the whole is 

 clean. 



