Saltpetre, conversion

Perchlorates. These may be present in appreciable quantity in conversion-saltpetre. The following method gives very accurate results 20 g. of the sample is heated to 545 in a covered nickel crucible and maintained for an hour at this temperature in a Gilbert furnace or electric furnace, to reduce Ihe perchlorate to chloride, which is then titrated with silver nitrate by Mohr s or Volhard s method. The chloride present in an unheated sample is deducted. Any chlorate or iodate present must also be allowed for, Lenze recommended heating for half an hour in a porcelain crucible at 580 to 600 . The first quarter of an hour is occupied in raising the temperature to the required point. At higher temperatures losses of chloride occur. Methods involving the addition of iron... 

Conversion Saltpetre.—To illustrate the use of Janecke s method of representation we may consider briefly the equilibria formed by the reciprocal salt-pairs (Na,K)—(NOgjCl) and water, which are of importance for the manufacture of conversion saltpetre, and which have been studied by Uyeda and by Reinders/ In this system no compounds or salt hydrates are formed. 

Peter Adrian Gadd (Birkala, 12 April 1727-Abo, ii August 1797) was professor of physics, chemistry and economics in Abo, Finland. His many publications, often in the form of dissertations by students (the British Museum has 36 of these), cover a variety of topics historical and general, on physical chemistry, on peat fuel, on mineralogy and metallurgy, on salts, agriculture, on the conversion of water into earth, and saltpetre. ... 

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