that the other silicides in commercial calcium carbide also behave in this manner it is plain that hydrogen silicide cannot occur in crude acetylene unless the gas is supposed to be hurried out of the generator before the alkaline water therein has had time to decompose any traces of the hydrogen silicide which is produced in the favouring conditions of high temperature sometimes prevailing. Mauricheau-Beaupré has failed to find silica in the products of combustion of acetylene from carbide of varying degrees of purity. He found, however, that a mixture of strong nitric and hydrochloric acids (_aqua regia_), if contaminated with traces of phosphoric acid, dissolved silica from the glass of laboratory vessels. Consequently, since phosphoric acid results from the phosphine in crude acetylene when the gas is passed through aqua regia, silica may be found on subsequently evaporating the latter. But this, silica, he found, was derived from the glass and not through the oxidation of silicon compounds in the acetylene. It is possible that some of the earlier observers of the occurrence of silicon compounds in crude acetylene may have been misled by the solution of silica from the glass vessels used in their investigations. The improbability of recognisable quantities of silicon compounds occurring in acetylene in any ordinary conditions of generation is demonstrated by a recent study by Fraenkel of the composition of the deposit produced on reflectors exposed to the products of combustion of a sample of acetylene which afforded a haze when burnt. The deposit contained 51.07 per cent. of phosphoric acid, but no silica. The gas itself contained from 0.0672 to 0.0837 per cent. by volume of phosphine.