MANUFACTURE, ETC., OF GUNPOWDER. 721 



both the decomposition of tbe saltpetre and the generation of gas, by 

 combining with the potassium of the saltpetre and liberating the oxy- 

 gen. Then, by heating the carbonic acid and nitrogen, it considerably 

 increases their volume, and consequently their explosive force. The 

 flash, and smoke, and the fouling of the gun, are the result of the de- 

 composition of the saltpetre, and consist of sulphates and carbonates 

 of potassa, resulting from the combination of potassium with the sul- 

 phur and carbon. The substances thus formed, swept out into the air, 

 become flame and smoke, or remain in the bore of the gun as fouling, 

 and it is these solid substances that blacken the faces of men engaged 

 in close conflict. 



Thus we see that of the materials of gunpowder saltpetre is the 

 most important. Both saltpetre and sulphur arrive in England in a 

 rough state, mixed with various impurities. It is generally the prac- 

 tice in private factories to purchase these materials after they have 

 been refined elsewhere; but atWaltham the refining process is carried 

 on within the works. By this means the materials are obtained of a 

 uniform quality and perfectly pure. The saltpetre comes from various 

 districts of India, chiefly from Bengal and Oude, where it is found 

 mixed with the soil, and as an incrustation on the ground. In India 

 it is boiled, and roughly-crystallized by evaporation. When it is re- 

 quired for use in the Gunpowder Factory, it is purified by a process 

 founded on the principle that hot water will receive in solution more 

 of the saltpetre than of the impurities mingled with it. The saltpetre 

 is boiled in water; the resulting solution is then filtered and allowed 

 to cool in large vats, at the bottom of which the pure saltpetre is de- 

 posited in fine crystals. It is then washed, dried, and stored in bins, 

 great care being taken that no sand or gritty particles are introduced, 

 as they might cause an explosion when under pressure at subsequent 

 stages of the manufacture, and the same precaution is taken with the 

 sulphur and the charcoal. It is believed that many of the explosions 

 which occur in private factories are caused by foreign substances being 

 present in the materials. 



The sulphur is all.of the best quality, imported from Sicily. It is 

 purified by a distilling process, which reduces it from its rough state 

 to masses of handsome yellow crystals. It is then pulverized by being 

 ground under iron runners, and sifted in a kind of revolving cylindri- 

 cal sieve, called a " slope-reel." The sulphur refining-house is, of the 

 whole factory, the least pleasant portion for a visitor, the air being 

 always tainted with the fumes of the sulphur, which are so strong as 

 even to burn and destroy the leaves of the trees near the building. 

 The management of the process is, however, by no means an unhealthy 

 labor. The workman last employed at it died as a pensioner at the 

 ripe old age of eighty, after having worked forty years in the refining- 

 house. 



The charcoal is all made on the spot, chiefly from wood imported 

 vol. vi. 46 



