NovEMBER r8, 1920 J NATURE 375 far more rapidly with a change of composition than do the other properties, diffusivity, tensile · strength, and. Young's modulus, which make up the thermal endurance of the glass. The coefficient of expansion of German laboratory glassware is something more than ro per cent. lower than that of English, and this fact alone would account for the breakage of the English glass with drastic heat treatment. There is no particular difficulty attached to the manufacture

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... f glass having a low coefficient of expansion and high thermal endurance, and we may take it that the English manufacturers have decided that the maximum resistance to attack by reagents is to be desired, and have, accordingly, sacrificed thermal endurance to a small extent in order to obtain the encouraging results outlined in Mr. Jenkinson's letter in NATURE of October 28. The whole question is largely one of general policy. If the chemists of this country pre fer to use a glass of higher thermal endurance but with less resistance to reagents, then I have little doubt that the British makers would supply it. E. A. COAD PRYOR. Milford, Park Road, Teddington, November 8.