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Analyßs. 4.67 29. To remove all doubt of the nature of the argill, it may be cfiayed with boiling cauftic fixed alkali, which diffolves argill, but not jar°onia. 30. The calx of iron, No. 19, fhould'then be roafted with a little wax for a quarter of an hour in a red heat, it will thereby be far reduced as to be magnetic, and contain about 70 per ct. of meraliic iron. ln many cafes where metallic fubftances are fully difengaged, and the folution coloured by them, they may be precipitated by the Pruffian alkali, as will be feen No. 95. Examinqtion of the UndiffolvedRefiduum, No. 3. 31. This refivloum wafhed, dried, heated to rcdnefs, and weighed, is firft to be efiayed for ftronthian, by treating it with fpirit of nitre 1,4, diluted with its own weight of water; whatever diffolves in this acid with eff erve feen ce, vvithout the afliftance of heat, is mild ltronthian 5 the folution fhould then be diluted and ftltrcd, and the depolite on'filtre wafhed, dried, and added to the remainder of the undiffolved reliduum. 32. The filtred liquor fhould then be gently evaporated, and fet to cryftallize, and the cryftals rediffolved in about their own weight of water, in the temperature of 66°, as cryftallization, and folution in this quantity of water, of that tempe rature, are additional proofs of ftronthian ; the folution of the cryftals fhould then be precipi tated by mild foda, the precipitate wafhed, dried, ignited for half an hour, and weighed. H h 2 33. After