256 



KNOWLEDGE. 



[NOVEMRFR 1, 1894. 



HOW NOXIOUS GASES AND VAPOURS 



FROM ALKALI AND OTHER WORKS ARE 



UTILIZED. 



By George McGowan, Ph.D. 



BLl'E-BOOKS and reports generally are not always 

 considered light and fascinating reading, but 

 anyone who is interested in the progress of 

 manufacturing chemistry will find much to repay 

 him in a perusal of the " Eeport on Alkali, etc., 

 Works" for last year (the thirtieth annual report), which 

 was presented in the spring to the Local Government 

 Board and to the Secretary for Scotland by the Chief 

 Inspector, Mr. A. E. Fletcher. The heading " Alkali, etc., 

 Works " comprises not merely alkali works proper, and 

 works for the preparation of sulphuric and other common 

 acids, but also those for tar distillation and for the manu- 

 facture of cement, sulphate of ammonia, chemical manures, 

 Venetian red, barium compounds, lead deposit, white 

 arsenic, nitrate and chloride of iron, felt, zinc, etc. As 

 a matter of fact, only a small minority of the works on 

 the register are alkali works. It would, of course, _ be 

 quite impossible to give within the limits of this article 

 anything like a detailed account of the important work in 

 which Mr. Fletcher and the other inspectors who are 

 associated with him are engaged, but a few of the salient 

 points in his report may be referred to with advantage. 



To begin with, there are now no less than lOlG works of 

 the above kind registered in England, Ireland and Wales, 

 and 127 in Scotland ; and in these 1703 distinct processes 

 of manufacture are carried on which come under the Act of 

 1892 ((.('., ll'Jo hi England, Ireland, and Wales, and 208 

 in Scotland). In the course of last year 5332 visits were 

 made to the various works by the inspectors, and 4974 tests 

 were carried out. " The tests above referred to are the 

 results of exact chemical determinations made of the 

 amount of acid gas or other matter in a measured volume 

 of the escaping air, taken either from the main culvert or, 

 'more usually, from the chimney itself. The analysis is 

 eitb.er made on the spot by the help of portable apparatus 

 arranged for the purpose, or the collected material is 

 taken°home for examination." The public generally will be 

 glad to hear that "the amount of noxious gas (escaping), 

 though now much below that of the legal standards 

 originally imposed, still gradually diminishes year by year." 

 Take first the case of hydrochloric or muriatic acid, 

 which is evolved in such enormous quantity in the manu- 

 facture of soda by the old or Leldanc method, and the escape 

 of which, before the Alkali Acts came into operation, made 

 the country into a desert for miles round an alkah work. 

 By the Att it is obligatory to condense 95 per cent, of the 

 hydrochloric acid generated — i.e., the manufacturer may 

 legally allow 5 per cent, of it to escape. But, taking the 

 average of all such works, only 1-72 per cent, escapes in 

 England, Ireland and Wales, and 3-32 per cent, in Scot- 

 land. This condensation has been found in the end to be 

 greatly to the advantage of the manufacturer, from the 

 value of the hydrochloric acid thus saved. To diverge for 

 a moment from the subject in hand, this seems to supply 

 an argument in favour of compulsory coal smoke consump- 

 tion in works generally. The consumption of coal smoke 

 is, of course, a much more difficult problem than the con- 

 densation of hydrochloric acid, and trade is at present not 

 in a condition to bear unnecessary restriction or legislation ; 

 but even allowing for all this, the question is one which well 

 deserves the practical attention of all who are interested 

 in sanitation, affecting as it does the whole urban community 

 more or less directly. 



To return to Mr. Fletcher's report. In the two well- 

 known methods of alkali manufacture, the newer ammonia- 

 soda process has almost outstripped the older Leblrmc 

 process, so far as the production of the main article, soda, 

 is concerned. But, as hydrochloric acid and bleaching 

 powder are bye-products of the Lrhlanc method, while 

 they are not obtained at all by the other, the former has 

 maintained its ground by their help. Some seven years 

 ago, as has already been described in Knowledge, a most 

 ingenious scheme was worked out by Mr. Chance, of 

 Oldbury, near Birmingham, for the recovery of sulphur 

 from alkali waste, immense heaps of which used to be 

 accumulated round alkali works (there being one and a 

 half to two tons of waste for every ton of soda produced 

 by the J.ehlanc method). This "waste" has constituted 

 in many cases a standing nuisance, from the fact that it 

 gradually undergoes decomposition by the atmosphere, and 

 more quickly by the acid vapours still found to some extent 

 in the neighbourhood of chemical works, the result being 

 that it evolves that nauseous and poisonous gas, sulphuretted 

 hydrogen. During the last few years many improve- 

 ments have been made in this (now spoken of as the 

 Chanre-Clnus) process. When it is mentioned that more 

 than 5,000,000 cubic feet of mixed air and sulphuretted 

 hydrogen (the latter being obtained from the " waste '" by 

 the above-mentioned method) are dealt with in this way 

 every twenty-four hours at one of the larger English alkali 

 works, when in full operation, some idea may be formed of 

 the care required to keep the numerous stopcocks, pipes, 

 and vessels tight— a task which is now satisfactorily 

 accomplished. " The applicatim of the process is now so 

 far advanced that already apparatus for treating the whole 

 of the tank waste of St. Helens and Widues has been con- 

 structed. Most of that produced on the Tyne is also 

 so treated, as is that at Oldbury and Wednesbury." 

 About 35,000 tons of sulphur are now recovered in this 

 way per annum. This constitutes a veritable triumph 

 in manufacturing chemistry. And the process is suscep- 

 tible of yet further improvement, as about 15 per cent, 

 of the sulphur contained in the " waste" under treatment 

 is still lost in the exit gases. None of it, however, is 

 allowed to e.scape into the atmosphere as sulphuretted 

 hydrogen, those exit gases being mixed with air and then 

 passed through a fire, with the result that all the 

 sulphurettel hydrogen present is converted into the much 

 less harmful sulphurous acid ; and this latter is to some 

 extent utilized in making sulphuric acid. 



The sulphate of ammonia produced in Great Britain and 

 Ireland amouated in 1893 to 152,762 tons (worth more 

 than £2,000,000 sterling), an increase of almost 3000 

 tons over ls92. Three-fourths of this was got from 

 the ammonia liquor of the gas works, the remainder 

 being from shale, iron, coke and carbonizing works. The 

 manufacture of this salt, which is of such supreme im- 

 portance for agriculture, used to be most offensive, from 

 the copious escape of sulphuretted hydrogen and other 

 noxious gases. Mr. Fletcher now writes with regard to 

 it : — " It is a matter of great satisfaction to be able to 

 report that no complaint has been brought during the past 

 year against any of these works," so much improved are 

 the methods of treatment. 



The arsenic works of Cornwall and Devonshire, where 

 white arsenic is prepared in large quantity by roasting 

 arsenical pyrites, were formerly the cause of frequent 

 litigation This arose from the alleged destruction of 

 cattle through eating grass said to have been poisoned by 

 arsenic which had escaped condensation in the long flues 

 used for the purpose (e.'itending in one case to over half a 

 mile in lengths After ineffectual attempts had been made 



