The fact of the matter is that the gas shell is not really a gas shell at all. It is nearly always a “liquid” shell and sometimes even a “solid” shell. The term “gas shell” is used because the liquid or solid contents are atomised by the explosion of the bursting charge or are distributed round in the form of such tiny particles or droplets, as the case may be, that they act almost as a gas. In the latter case they form what might be described as a mist or smoke, but with this difference from ordinary smoke--that the gas mist or smoke is generally, though not always, invisible. Just imagine what would happen supposing a shell were filled with water. Burst such a shell with a sufficiently big charge of high explosive and all the water would be distributed into the air in the form of such finely divided spray that it would form a mist. This mist would either vapourise into the atmosphere completely or hang about like a cloud, according as the air was dry or moist. In any case, if the burster were big enough no water would be spread on the ground; nor would any big drops be formed. This is just what happens with any of the poisonous materials filled into a shell. Indeed if the burster were big enough and carefully chosen it would be possible to form a “gas” with treacle. With a volatile material like gasoline on the other hand all that would be needed would be a burster just big enough to open the shell. It can be seen therefore that the choice of materials for gas shell is practically unlimited and is governed only by their being poisonous enough and by the ease of production. Another thing in which the gas shell has the advantage over the cylinder gas is in getting surprise, which is naturally much easier to effect with shell. By the way, if the reader wishes to be counted among those who knows, he will always speak or write the plural of shell without adding a final “s.” To talk of a number of shells is very civilian. As I pointed out before, we were expecting something new to happen in the gas-shell line during the whole of 1916, and had an idea that the new arrival would be something of a cyanide nature--possibly prussic acid itself. When it did come, however, it proved to be a liquid filling closely related chemically to phosgene and to the K-Stoff, which I have previously described. These new gas shell were the first of the present series of German gas shell, which are all distinctly marked with coloured crosses and named accordingly. These particular shell were the Green Cross Shell, a green cross being painted on the base of the cartridge or on the side of the shell or sometimes on both. They made their appearance on the Somme Front about a fortnight after the battle had started--that is, about the middle of July, 1916--though a few of them had been used against the French on the Verdun Front sometime in June.