and Detonating Matches. 123 



crystals arc dried, fused in an iron pot at a temperature of from 

 500 to 600 Fahrenheit, and cast into moulds. The cakes are 

 preserved in casks. 



About the period of 1794 and 1795, under the pressure of 

 the first wars of their revolution, the French chemists employed 

 by the government contrived ah expeditious, economical, and 

 sufficiently effective mode of purifying their nitre. It must 

 be observed that this salt, as brought to the gunpowder-works 

 in France, is in general a much cruder article than that im- 

 ported into this country from India. It is extracted from the 

 nitrous salts contained in the mortar-rubbish of old buildings, 

 especially those of the lowest and filthiest descriptions. By 

 their former methods the French could not refine their nitre in 

 less time than eight or ten days ; and the salt was obtained in 

 great lumps, very difficult to dry and divide : whereas the new 

 process was so easy and so quick, that in less than twenty-four 

 hours, at one period of pressure, the crude saltpetre was con- 

 verted into a pure salt, brought to perfect dryness, and in such 

 a state of extreme division as to supersede the operations of 

 grinding and sifting, whence also considerable waste was 

 avoided. 



The following is a brief outline of this method, with cer- 

 tain improvements, as now practised in the establishment of 

 the Administration des poudres et salpetres, in France. 



The refining boiler is charged over night with 600 kilo- 

 grammes of water, and 1200 kilogrammes of saltpetre, as 

 delivered by the salpetriers. No more fire is applied than is 

 adequate to effect the solution of this first charge of saltpetre. 

 It may here be observed, that such an article contains several 

 deliquescent salts, and is much more soluble than pure nitre. 

 On the morrow morning the fire is increased, and the boiler 

 is charged at different intervals with fresh doses of saltpetre, 

 till the whole amounts to 3000 kilogrammes. During these 

 additions, care is taken to stir the liquid very diligently, and 

 to skim off the froth as it rises. When it has been for some 

 time in ebullition, and when it may be presumed that the 

 solution of the nitrous salts is effected, the muriate of soda is 

 scooped out from the bottom of the boiler, and certain affu- 

 sions or inspersions of cold water are made into the pot, to 



