ON THE UTILIZATION OF WASTE. 405 



of iron and a cyanide of potassium. The nitrogen combines with the 

 carbon and forms cyanogen ; and then the cyanogen combines with the 

 iron and the potassium, and forms this prussiate of potash. This salt 

 is very extensively employed because it is the source of Prussian blue. 

 I have here a solution of iron rust which I add to this solution of the 

 yellow salt. You see immediately that a copious precipitate of Prussian 

 blue is produced — that beautiful colour which we employ so extensively. 

 Now, if you pass chlorine through yellow prussiate of potash, you re- 

 move one equivalent of potassium, and then you get this other salt, the 

 red prussiate of potash, which, though it differs from the other merely in 

 containing one equivalent of potassium less, yet is changed in its che- 

 mical characters considerably. The yellow salt is not poisonous, but 

 the red salt is intensely poisonous. This also with another salt of iron 

 — a proto-salt of iron — forms Prussian blue. If I put some of this red 

 salt into the water, and add a lower oxide of iron, it forms a Prussian 

 blue of a characteristic brilliancy, which enables it to be used in many 

 cases in preference to that which is produced from the ether salt. 



White Gunpowder. — If I take 28 parts of that yellow prussiate, 

 23 parts of cane sugar, 49 parts of chlorate of potash, and then sieve 

 them so as to mix them together, we get a description of gunpowder. 

 This gunpowder has certain advantages even above ordinary gun- 

 powder. Weight for weight, it forms nearly double the volume of 

 gas that common gunpowder yields ; and it leaves less residue behind. 

 Although you may think the ash considerable, it is still less in quantity 

 than the amount which is left by the ordinary gunpowder. But the 

 temperature of the flame on ignition is not so high ; so that, although 

 the white gunpowder produces double the amount of gas, that gas is 

 not heated so much, and therefore does not expand so much as in the 

 case of ordinary gunpowder, and the projectile force of this white gun- 

 powder has not answered the expectations formed of it. Still, it is so 

 exceedingly easily made — by simply taking these materials, prussiate 

 of potash, chlorate of potash, and sugar, sieving them separately so as 

 to get them fine, and then sieving them in their proportions together 

 so as to get them mixed, that it may have some advantages. There is 

 required none of the mechanical appliances necessary in the manufac- 

 ture of ordinary gunpowder, such as the milling, and glazing, and gra- 

 nulation, which make its manufacture so troublesome and expensive. 



Bones. — Bags and bones are naturally associated in one's mind. The 

 same collector collects both ; although I confess I am somewhat sorry 

 for their association to-day, because the chemistry of bones is so exten- 

 sive that I scarcely know how to handle it in half a lecture. I must 

 therefore pass over their known applications — the applications which 

 are so familiar to you. I can say nothing of their use as a manure, 

 either in the ground or subdivided state, or as they are often used, after 

 being treated with sulphuric acid, under the name of superphosphate of 

 lime. I cannot even, interesting as it is, dwell upon the fact that 



