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Show SAVING ROOIV1 j; Merchant Did you post my letter f as I told you, John? i John Yes, sir, but I had it weighed f. first, and as It was double weight 1 put another stamp on it. k Merchant That's right. Only I hope you didn't put the oxtra stamp on so ( that it would obliterate the address. ' h John Indeed. I didn't sir. I just put ( it on top of the other stamp so as to save room. St. Louis Star. ' s ACID FROM AIR .t All the explosive used in this world-war are formed from such ap- t u parently harmless bodies as cotton, ' f glycerine, and tar products by treat- ' ing them with nitric acid, the strength ' of which has to be maintained by admixture with sulphuric acid. ! j Until quite lately the nitric acid es- i JB sential for tho production of tho ex- IB plosive now in use could be made flB only by distilling such nitrates as '. I'lB those of potassium and sodium with f jlB sulphuric acid, and if science had still : fJB been dependent on this source, all the ; NB powers engaged in the present war would have been stalemated by want ; jiB of explosives, so enormous has been t JB the amount of acid used. During tho last few years, however, I I methods have been discovered for 1 jflB making nitric acid from tho air, and B at tho present time, wherever cheap ; B water-power can be obtained for gen iBj erating electricity the acid is being , gH producted in sufficient quantities to ( B make up the necessary amount. ; H |