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Mr. C.J. JACKAMAN (Member of Council) said that the Institution was very greatly indebted to the author of this Paper. He had listened with great appreciation to what the author had said, and it had given rise to a number of questiom in his mind, which he would refrain from asking because there would not be time to answer them. But the author had covered many if not all the most salient features relating to aerodromes. His paragraph headed "A Nationa1 Necessity" was most opportune, as were also his remarks on accessibility.
Sir,-In the discussion on Mr. Gueritte’s illuminating paper, a speaker suggested that quicker hydration of the cement was partly responsible for the increase in strength of vibrated concrete. I think there is a great deal in this suggestion. The formation of colloid round a cement grain hinders the further access of water, and delays hydration. If this colloid could be removed, and fresh water allowed to reach the cement, a more uniform and richer colloidal solution would result, and, finally, a better gel. Increasing the period of mixing does this to some extent, and results in stronger concrete. The extreme rapidity and small magnitude of the motion in vibrating concrete is an infinitely more efficient method of tearing the colloid skin from its parent cement grain, and enabling fresh water to carry on the process of hydration. The formation of a very rich colloidal solution is shown by the quickness with which the concrete jellifies and stiffens enough for forms to be removed. If samples of vibrated andunvibrated concrete were tested shortly after casting, the vibrated concrete would show a very much higher percentage of water held chemically and colloidally, which is one way of expressing a stronger concrete. The reduction of voids does, of course, play its part; but is not responsible for all the increase of strength; and the rich colloidal solution forms a lubricant which facilitates compaction.
THIS paper gives a brief description of the methods adopted in the construction of ten blocks of 320 industrial dwellings, known as Evelyn Court, Hackney, and one block of 21 dwellings at Berners Street, Stepney. These flats are constructed in reinforced concrete, by patented methods which had not been used previously in this country. F.S. Snow