126 SCIENTIFIC AMUSEMENTS. 



leaden pipes, or being stored in leaden cisterns. Such water is 

 very objectionable, being often highly injurious to health; the 

 presence of any serious contamination of this kind may be detected 

 by a comparison colour test, worked somewhat after the fashion of 

 the last experiment. Procure two test-tubes as long as possible, 

 better still, two glass cylinders a foot high, standing on flat bottoms 

 (fig. 40) ; fill each with the water to be tested, and add two or 

 three drops of dilute pure hydrochloric acid to each. To one of 

 the cylinders now add a teaspoonful of freshly prepared clear 

 solution of sulphuretted hydrogen, and shake up the water to pro- 

 mote proper intermixture. If there is no lead or copper in the 

 water, both cylinders will appear alike when you look downwards 

 through the long columns of fluid (with a piece of white paper 

 underneath) ; but if there is any poisonous metal present, a more 

 or less marked difference in colour will be noticed, a distinctly 

 yellower or browner shade being communicated to the contaminated 

 water by the sulphuretted hydrogen than it originally possessed/' 5 " 

 If the test is to be made an excessively delicate one, a large bulk 

 of water should be treated with a few drops of hydrochloric acid, 

 and evaporated in a clean glass or porcelain vessel on a water-bath 

 (Expt. 89), until reduced in volume to such an extent as only just 

 to fill the two cylinders ; obviously, if the water has been reduced 

 to one-tenth of its original bulk by evaporation, anything present 

 in the water will be concentrated tenfold, and the test accordingly 

 made ten times as delicate. 



Expt. 126. To detect Copper and Lead in Pickles, Preserved 

 Provisions, &c. Copper compounds are sometimes employed to 

 give a bright green tint to preserved vegetables, such as tinned 

 peas, &c., and certain kinds of pickles. In the latter case tho 

 presence of copper can generally be detected by filtering some of 

 the vinegar clear into a test-tube and adding solution of sul- 

 phuretted hydrogen, when a considerable darkening or formation 

 of black precipitate will take place. To find the copper in the 

 solid vegetables, these should be burnt to ashes over a spirit lamp 

 or Bunsen lamp in a little tray of platinum made by bending up 

 the sides of a slip of platinum foil, the tray being supported by a 

 stand or tripod, preferably resting on a triangle made by threading 

 an iron wire through three bits of clay tobacco pipe stem (fig. 65). 

 The ashes are treated with a few drops of diluted nitric acid, and 

 the liquid filtered through a small filter; a few drops of the 



* Good water may naturally have a slightly yellowish shade when thus 

 viewed, owing to traces of clayey matter, peat, &c., being present in quantity 

 too small to affect the quality of the water materially, but large enough to 

 be just visible to the eye when thus examined. 



