It is absolutely essential that the water impregnated with sulphuretted hydrogen, when employed as a test for detecting very minute quantities of lead, be fresh prepared; and if sulphate of potash, or sulphate of soda, be used as tests, they should be perfectly pure. Sulphate of potash is preferable to sulphate of soda. It is likewise advisable to act with these tests upon water concentrated by boiling. The water to which the test has been added does sometimes appear not to undergo any change, at first; it is therefore necessary to suffer the mixture to stand for a few hours; after which time the action of the test will be more evident. Mr. Silvester[26] has proposed gallic acid as a delicate test for detecting lead. FOOTNOTES: [11] Dalton, Manchester Memoirs, vol. iv. p. 55. [12] Marsden's History of Sumatra. [13] Manchester Memoirs vol. x. 1819. [14] Observations on the Water with which Tunbridge Wells is chiefly supplied for Domestic Purposes, by Dr. Thomson; forming an Appendix to an Analysis of the Mineral Waters of Tunbridge Wells, by Dr. Scudamore. [15] It is absolutely essential that the tests should be pure. [16] Philosophical Magazine, vol. xv. p. 252. [17] Transactions of the Royal Society of Edinburgh, vol. viii. p. 259. [18] Sir G. Baker, Med. Trans. vol. i. p. 280. [19] Lamb on Spring Water. [20] Medical Trans. vol. i. p. 420. [21] Van Swieten ad Boerhaave, Aphorisms, 1060. Comment. [22] Medical Comment. Dec. 2, 1794. [23] Lambe on Spring Water. [24] See An Analysis of the Mineral Waters of Tunbridge Wells, by Dr. Scudamore, p. 55. The application of the sulphuretted hydrogen test requires some precautions in those cases where other metals besides lead may be expected; because silver, quicksilver, tin, copper, and several other metals, are affected by it, as well as lead; but there is no chance of these metals being met with in common water.--See _Chemical Tests_, third edition, p. 207. [25] Analysis of Tunbridge Wells Water, by Dr. Scudamore, p. 55. [26] Nicholson's Journal, p. 33, 310. _Adulteration of Wine._ It is sufficiently obvious, that few of those commodities, which are the objects of commerce, are adulterated to a greater extent than wine. All persons moderately conversant with the subject, are aware, that a portion of alum is added to young and meagre red wines, for the purpose of brightening their colour; that Brazil wood, or the husks of elderberries and bilberries,[27] are employed to impart a deep rich purple tint to red Port of a pale, faint colour; that gypsum is used to render cloudy white wines transparent;[28] that an additional astringency is imparted to immature red wines by means of oak-wood sawdust,[29] and the husks of filberts; and that a mixture of spoiled foreign and home-made wines is converted into the wretched compound frequently sold in this town by the name of _genuine old Port_.