158 SCIENTIFIC AMUSEMENTS. 



solution some hydrochloric acid; this will act on the soap, and 

 liberate therefrom the " fatty acids " which, together with soda, 

 constitute the soap. The exact nature of these fatty acids depends 

 on the materials used for preparing the soap, being somewhat 

 different according as tallow, olive oil, palm oil, &c., are employed ; 

 but in any case they will not dissolve in the watery fluid, and conse- 

 quently gradually separate as an oily layer on the surface. Enough 

 hydrochloric acid should be added to make the liquid bright red 

 when a little tincture of litmus is added, and the whole well shaken 

 up ; if this hot fluid be poured out into a saucer or basin, and left 

 to cool, the fatty acids will by and by set to a solid or pasty 

 mass, according to their nature. 



Expt. 171. To precipitate Fluid Quicksilver from Solution. 

 Boil half an ounce of granulated tin (Expt. 16) with strong 

 hydrochloric acid for half an hour ; a liquid will be formed con- 

 taining a compound termed stannous chloride or chloride of tin. 

 Now dissolve in water a few grains of corrosive sublimate (or 

 mercuric chloride), and add to the solution some of the stannous 

 chloride solution ; the first effect will be that a white precipitate 

 of a compound called calomel will be produced; but on adding 

 more stannous chloride solution, and boiling, this will turn grey, 

 and ultimately will become converted into minute globules or 

 drops of fluid quicksilver. In this experiment the action is obviously 

 closely akin to that whereby gold is separated from solution of 

 chloride of gold (Expt. 135). 



Expt. 172. Another way of reproducing Mercury from Solu- 

 tion. Take a penny-piece, or a fragment of brass or copper, and 

 rub it over with a solution of nitrate of mercury (Expt. 166), using 

 an old tooth-brush or a piece of rag dipped in the fluid as a rubber; 

 the copper present in the metal employed will act on the nitrate 

 of mercury, forming nitrate of copper (Expt. 134), and precipitat- 

 ing metallic mercury, which will adhere to the metal and whiten 

 its surface, making it resemble silver ; the white coating, however, 

 is not as permanent as actual silvering, but by and by disappears, 

 partly because the mercury gets rubbed off, and partly because it 

 gradually sinks into the interior of the solid metal. 



Caution. Mercury has a strong tendency to adhere to gold and 

 silver articles, and also to penetrate into them if it come in contact 

 with them externally, rendering them brittle in so doing (compare 

 Expt. 69). Whenever any experiments are made involving the 

 use of quicksilver, care should be taken that the quicksilver 

 should not be splashed over rings, watch chains, &c., otherwise 

 these may be seriously injured, and rendered so brittle as to break 

 readily. Should a little mercury get splashed on to a gold ornament, 



