314 SCIENTIFIC RECREATIONS. 



has been soaked in phosphate of ammonia, which is very inexpensive, and 

 easily procured. 



For preparing cool drinks in the summer ammoniacal salts are very 

 useful ; some nitrate of ammonia mixed with its weight in water, produces a 

 considerable lowering of the temperature, and is very useful for making ice. 

 Volatile alkali, which is so useful an application for stings from insects, is a 

 solution of ammoniacal gas in water, and sal-volatile, which has such a 

 refreshing and reanimating odour, is a carbonate of ammonia. We often 

 see in chemists' shops large glass jars, the insjdes of which are covered with 

 beautiful transparent white crystals, which are formed over a red powder 

 placed at the bottom of the vase. These crystals are the result of a 

 combination of cyanogen and iodine. Nothing is easier than the preparation 



Fig. 302.- -Experiment with ammonium. 



of iodide of cyanogen, a very volatile body, which possesses a strong tendency 

 to assume a definite crystalline form. We pound in a mortar a mixture of 

 50 grams of cyanide of mercury, and 100 grams of iodine ; under the action 

 of the pestle the powder, which was at first a brownish colour, assumes a 

 shade of bright vermilion red. The cyanogen combines with the iodine, 

 and transforms itself into fumes with great rapidity. If the powder is 

 placed at the bottom of a stoppered glass jar, the fumes of the iodide of 

 cyanogen immediately condense, thereby producing beautiful crystals which 

 often attain considerable size (fig. 303). Cyanogen forms with sulphur a 

 remarkable substance, sulpJio-cyanogeu, the properties of which we cannot 

 describe without exceeding the limits of our present treatise ; we shall there- 

 fore confine ourselves to pointing out one of its combinations, which is well 

 known at the present day, owing to its singular properties. This is sulpho- 

 cyanide of mercury, with which small combustible cones are made, generally 



