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69to reach our compressors without detection, such however has happenedmore than once and although I am glad to say no serious injury hasever occurred through ignition of gases and consequent explosion in acylinder, we have had alarming experiences, and narrow escapes fromserious accidents. I may point out that these are accidents which couldonly occur during compression, and are consequently risks to which weand not the customer are exposed. Such experience is now very rareindeed, as the danger is more generally known, and I may add that asan absolute safeguard in addition to colour we now ma'ke all connectionsfor oxygen and coal gas different and consequently non-interchangeable,and when this is universally adopted, the real and I may say onlyelement of danger in our business will be practically done away with."" How do you account for such explosions of coal gas and oxygen ? "" That is a difficult question to answer, they are undoubtedly due tosufficient heat being generated in some portion of the cylinder tocause ignition of the two gases."" It may be dueto a variety of causes. The actual compression of thegases causes a certain amount of heat, but this alone is not sufficient toexplain the occurrence. It can only be that (owing to, in part, thecompression, but to a much larger extent—the friction caused in thevalve passages which may be full of oil or hydro-carbon deposit, and thesudden impact of the gas rushing into the cylinder) sufficient heat iscaused locallyto ignite an explosive re-action of gases, and of course themoment ignition takes place enormous heat and pressure iscreated insidethe cylinders. A cylinder which has been long used for coal gas lendsitself most to such accidents, as it would be coated inside with a lining othydro-carbon deposit."" When oxygen escapes from a cylinder in any quantity, it is noticedthat the flow is very uneven. How do you account for this ? "" This should only occur when oxygen is allowed to escape veryrapidly from the cylinder and then the explanation is very simple. It isjust the reverse of what takes place when the gas is compressed. Thehighly compressed gas in the cylinder has by the time it is used cooleddown to the temperature of the surrounding atmosphere. This largevolume of gas when expanded out of the cylinder, abstracts the heatfrom the surrounding atmosphere, with the result that such an intensecold is generated immediately round the cylinder as to create ice fromthe moisture present and this ice getting into the valve passages c auses