Of course over a wide area all metal work is thickly tarnished, and this might be a danger in the case of telephone instruments and other delicate appliances, except that the exposed parts are always kept slightly oiled and then cleaned thoroughly after the attack. The same thing is done with rifles and machine guns and their ammunition, and with the clinometres, fuses and breech mechanism of guns and trench mortars. Since this war started very little difficulty has occurred through corrosion, but the chief thing is to clean off the grease and reoil all metal parts exposed to the gas immediately after the attack is finished, otherwise the greasy surface seems to hold the gas or the acid it engenders, and allows it to eat in at its leisure. During the attacks of 1916 the alarm arrangements worked very well, and the Strombos Horns in particular justified their use. Even above the noise of machine-gun fire and the bursting of shells their shrill, unmistakable note could be heard for long distances, giving warning to all troops on the flanks and in the rear. There were very few instances where they were not let off in time and the sentries posted over them apparently knew their jobs better, for instance, than one man who was questioned on the subject. This particular sentry was asked by a noncommissioned officer going the rounds in the trenches what he would do in the event of a gas attack being made. “Oh,” replied the bright boy, “that’s easy. If any gas comes over it blows the horn and I call the platoon sergeant and tell him about it.” A much more conscientious sentry over a Strombos Horn had been told to be particularly on the lookout for a gas attack, as one was expected at any time. The officer on duty, going round about midnight, heard a suspiciously regular sound coming from one of the fire bays, and thinking that one of the sentries was indulging in a stolen forty winks he cautiously rounded the traverse. Here he found the sentry lying on the top of the parapet staring into the darkness and going sniff, sniff, sniff with his nose. Being asked more forcibly than politely what was the matter with him the man replied: “I’m sniffing for gas.” Sniff, sniff, sniff. “Can you smell any?” “No, sir; but I want to smell it if it does come, as I’m a gas sentry and the leftenant told me always to keep smelling for gas.” Sniff, sniff, sniff. The job of seeing that the air cylinders of the Strombos Horns are kept at their full pressure is intrusted to the divisional gas noncommissioned officers, who go round periodically with pressure gauges and test them out. If they fall below a certain pressure they are replaced at once by fresh ones from the divisional store. Some Australians going up the line one night were carrying a number of such cylinders for replacement, when one of them got turned on accidentally and they didn’t seem able to stop it. A passing officer hearing the hissing noise called out: “What have you got there?”