THE BOOK OF THE LANTERN. 35 



books ; but, as a matter of fact, the exact proportion is not 

 of very great consequence. Indeed, it would seem that if 

 the crystals of potash have mixed with them just sufficient 

 of the black manganese to dirty them well, the mixture 

 will be effective. 



Oxygen gas can be generated from the chlorate alone, 

 but the action is so uncertain that the salt is always mixed 

 with manganese, oxide of iron, or sand. What action the 

 manganese has upon the mixture is not known, for it is 

 a curious fact that, after the operation is over, it remains 

 unchanged, so that it is possible, if one cared to take the 

 trouble, to preserve it and use it over and over again. 

 Where manganese is difficult to obtain, this method may 

 be adopted, but in most towns it can be procured at such 

 a cheap rate that such a course would simply represent a 

 waste of time and trouble. 



The greatest care should be exercised in procuring both 

 components of the oxygen mixture in an unadulterated 

 state. The ordinary commercial chlorate is quite good 

 enough for the purpose, and although it has the disadvan- 

 tage of being contaminated with a certain amount of free 

 chlorine which is given off in gas-making, it would be 

 a useless expense to employ the pure salt, as used for 

 medicinal purposes. Moreover, the chlorine can be got rid 

 of, as we shall presently see, by simple means. But in 

 most samples of commercial chlorate there are to be found 

 certain foreign bodies, such as bits of straw, bits of wood 

 (from the casks in which the chlorate is originally sold), 

 and other specimens of matter in the wrong place, which 

 would be prejudicial to the operation of gas-making, and, 



D2 



