208 



KNOWLEDGE 



[November 1, 1892. 



" He died the 21st April, 1798, in the 69th year of 

 his age. 



" And in the same spot united in death as in life, the 

 hody of Gilbt. Michell. Esqr., Brother to the above, lies 

 interred, a gentleman whose peculiar urbanity of manners 

 and suavity of temper, attracted the love and esteem of all 

 who knew him. In the conscientious discharge of all 

 those offices which characterize the honest and good man. 

 He was the counterpart of the above : united in the closest 

 bonds of fraternal love. The union of virtuous and phil- 

 anthropic sentiment was not less strict. For more than 

 twenty years He was an ornament to and a valuable 

 resiant [ ! ] of this parish. He died the 15th Novr., 1792, 

 aged 66. 



"Gratitude and affection have erected this tablet to 

 their memory." " 



BYE-PRODUCTS «'«'«'« WASTE-PRODUCTS. 



By Vaughan Coenisu, M.Sc, F.C.S. 



THFj well-known Leblanc process for making soda 

 came into use about one hundred years ago. Till 

 its introduction the alkali required in various 

 manufactures was nearly all obtained from the 

 ashes of plants. Potash, the alkali obtained from 

 land plants, was more plentiful than soda, which is obtained 

 from the ash of sea plants. The sodium of the soda 

 yielded by sea plants is contained in the sea in the form of 

 common salt. By Leblanc's process the soda is prepared 

 directly from common salt, thus avoiding the tedious and 

 uncertain collection of sea-weed. The first impetus which 

 the new method received was in 1793, when France found 

 herself deprived of alkali, which used to come chiefly from 

 Eussia and America. How serious was the inconvenience 

 thus caused may be readily imagined, since the manu- 

 facture of soap and of glass is dependent on a supply of 

 alkali. 



Leblanc's process for preparing soda direct from salt 

 relieved France from an industrial difficulty. It also 

 changed the relative importance of the two alkalies, making 

 soda much cheaper and more plentiful than potash. 

 Leblanc himself died in a French workhouse, but manu- 

 facturers on this side of the Channel were more fortunate, 

 and many of them accumulated wealth as rapidly as the 

 iron-masters did in later times. The demand for soda was 

 unlimited, and the sole object of the manufacturer was to 

 produce as much of the article as possible. The materials 

 lor the manufacture are the following, viz. : — first, salt and 

 sulphuric acid, which react on one another, producing 

 " salt cake " (sulphate of soda) and hydrochloric acid gas ; 

 secondly, limestone and coal, which, being heated with 

 the sulphate of soda, produce the required alkali, carbonate 

 of soda, more commonly known simply as " soda." In this 

 second reaction the final products, besides soda, are 

 sulphide of calcium and carbonic acid gas. Leaving out 

 of account this last substance, the product of all com- 

 bustion, we see that in the manufacture of soda the 

 waste products are, or were, two, viz. : — hydrochloric acid 

 gas and sulphide of calcium, or " alkali-makers' waste." 

 The former substance was allowed to escape into the 

 atmosphere, killing all vegetation for miles around, whilst 

 the latter accumulated in vast heaps in the neighbourhood 



* T}ie Rev. F. R. Grenside, M.A., Queen's College, Cambridge, the 

 jiresent Rector of ThornliiU, his kindly furnished me with this copy 

 uf t'lc nV-MU-iriiil tablet. In sending it lie remirk'ii that it is impossible 

 Tiot to be struck with the fine stylo in which it is written It is 

 likely that the mison is rc3])onsiblc both tor tin' imiictuation and the 

 .spelling. 



of the works, constantly undergoing decomposition through 

 the action of air and moisture, and poisoning the atmos- 

 phere with fumes of sulphuretted hydrogen, besides 

 polluting the streams with the poisonous drainage of the 

 decomposing mass. The alkali-maker cared for none of 

 these things, and the Government found it necessary to 

 legislate in order to protect the health and property of 

 the manufacturer's neighbours. The manufacturers were 

 compelled to condense and retain the fumes of hydrochloric 

 acid, though the decomposition from the "waste" continued 

 10 be a nuisance to the neighbourhood. The alkali-maker 

 being obliged to go to the expense of collecting the 

 hydrochloric acid, set to work to compensate himself for 

 the outlay involved, by utilizing the formerly waste pro- 

 duct hydrochloric acid, which now became a bye-product 

 of the manufacture. More recently a process has been 

 introduced for recovering the valuable sulphur from the 

 sulphide of calcium. Employing the same materials as 

 formerly (salt, sulphuric acid, limestone, and coal), the 

 principal products of the modern manufacture are three 

 instead of one as formerly — that is to say soda, hydro- 

 chloric acid, and sulphur, instead of soda only. It is a 

 singular fact that at the present time the Leblanc manu- 

 facturer produces the soda at a loss, while the bye- 

 products yield a profitable return, sufficient to pay him 

 the interest on the capital which is locked up in the huge 

 plant of the alkali works. From the hydrochloric acid 

 chlorine is now made, and the chlorine gas, passed over 

 dry slacked lime, forms the bleaching powder which is 

 used in enormous quantities for whitening cotton and 

 other goods. Large quantities are also used for disin- 

 fecting purposes ; the recent cholera scare, by the way, 

 sent the price up in a manner most satisfactory to the 

 makers. At first one of the chief items of expense in the 

 manufacture of bleaching powder was the consumption of 

 manganese dioxide, employed to set free chlorine gas from 

 the hydrochloric acid. This is now "regenerated" by 

 Weldon's process, in which the chloride of manganese 

 formed in the reaction is acted upon by air and steam in 

 the presence of lime, the final "waste" material being 

 calcium chloride. Similarly, in Chance's process for the 

 recovery of sulphur from the alkali-makers' wj,ste, the 

 same substance, calcium chloride, is the final waste 

 product. Chance's process is conducted in two stages ; 

 first, the partial oxidation of the sulphide of calcium by air 

 and steam, and secondly, the decomposition of the oxidized 

 product by hydrochloric acid, in which sulphur separates 

 out and calcium chloride is formed. Calcium chloride is 

 a material for which there are but few applications, and it 

 is practically " waste." The loss of calcium is not of 

 importance, since abundance of the useful compounds of 

 this element can always be obtained from natural sources, 

 such as limestone. But the chlorine is valuable, and many 

 efforts have been made to recover this element from 

 calcium chloride. It is quite possible to set the gas free, 

 but hitherto a sufficiently cheap and simple process has 

 not been found, although much attention has been 

 devoted to a problem the solution of which may yield a 

 large fortune. Calcium chloride is indeed the final waste 

 product in a large number of chemical processes. 



We have mentioned that the soda made by the Leblanc 

 manufacturers is now produced at a loss. This is due to 

 the introduction of another method of manufacture, known 

 as the ammonia-soda process, in which a purer product, 

 commanding a higher price, is simply and quickly obtained. 

 In this process carbonic acid gas is passed through watei 

 which contains, dissolved, both common salt and ammonia. 

 Soda, in the form of the bicarbonate, is deposited from the 

 solution in crystals, the carbonic acid uniting to the base 



