becomes turbid if exposed to the air; and on evaporating it, the residuum dissolves in weak nitric acid with brisk effervescence. Captain Yorke estimates the quantity dissolved when the water is saturated at a 10,000th part.[1]
By far the greatest part of the lead, however, which disappears, will be found in the white pearly crystals. This crystalline powder is not,—as alleged by Guyton-Morveau, and after him by some systematic writers, a hydrated oxide of lead, but, as stated above, a particular variety of carbonate, containing more hydrated oxide than exists in common white lead. At first I thought it was neutral carbonate. Captain Yorke was led to suppose it hydrated oxide. In 1842 I found that, if it be exposed for some time to the action of aërated water after the lead has been removed, it invariably consists of two equivalents of neutral carbonate and one of hydrated oxide.
It will be inferred from the preceding facts, that distilled water for economical use should never be preserved in leaden vessels or otherwise in contact with lead. Even the distilled water of aromatic plants should not be so preserved, because the essential oil which communicates to them their fragrance does not take away the power which pure distilled water possesses of acting on lead. This fact was first announced in the second edition of the present work. A druggist in Edinburgh requested me to examine a reddish-gray crystalline, pearly sediment formed copiously in a sample of orange-flower water. I found this to be carbonate of lead coloured by the colouring matter of the water, and obviously produced by the action of the water on lead solder used instead of tin solder, and coarsely and liberally applied to the seams of the copper vessel in which the water had been imported from France. The filtered fluid did not contain a particle of lead. The same observation has been since made by a French pharmaceutic chemist, M. Barateau, who seems at a loss, however, to account for the formation of the carbonate of lead.[2] It appears from an inquiry of MM. Labarraque and Pelletier, conducted at the request of the Prefecture of Paris, that the orange-flower water, which is extensively used there, is often adulterated with lead in solution. They impute this to careless distillation; for then some of the decoction is driven over with the distilled liquid, and consequently produces a fluid which becomes acetous by keeping and dissolves the lead solder of the estagnons or copper vessels. Pure orange-flower water does not acidify by keeping.[3] M. Chevallier in a more recent investigation arrived at the same results, and found that few specimens of the orange-flower water of Paris were altogether free of lead.[4] In none of these inquiries have the authors adverted to the action of pure water in forming carbonate of lead.
- ↑ The statement here given of these phenomena is somewhat different from what is contained in the last edition of this work. The present account is derived from ulterior experiments, partly published in my paper in the Edinburgh Transactions. The discrepancies formerly prevailing between my own researches and those of Captain Yorke are now completely reconciled.
- ↑ Journal de Chim. Méd. ix 714.
- ↑ Annales d'Hyg. Publ. et de Méd. Lég. iv. 55. 1830.
- ↑ Journal de Chim. Médicale, ix. 716. This adulteration has likewise since then attracted attention in London. See British Annals of Medicine, 1837, i. 15.
