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silicates have a higher refractive index than the silicates of other metals, the appearance of lead glazes being thereby enhanced. The compulsory adoption of leadless ware would therefore entail the loss of the highest-class trade against competitors who were not so handicapped. A compromise has been suggested in the introduction of lead into glazes as insoluble bisilicate. Experience has shown that this eliminates plumbism, but many potters still maintain that the use of " fritted " lead does not con- duce to a high standard of appearance. They prefer to use " raw 5: lead in the form of red or white lead, and to pay compensation to their workers when plumbism occurs. The history of the movement against lead poisoning is quite modern, and is concerned as much with white lead 76 CERAMIC CHEMISTRY. and paints as with pottery. But we must confine ourselves here to consideration of the last. In 1891 Oliver's Goulstonian lectures, subsequently published in book form, dealt with the subject as studied by him at Newcastle, a centre of white lead manufacture. Seven years later Thorpe and Oliver, appointed by the Home Office, recommended the compulsory adoption of fritted lead glazes having a solubility of less than 2 per cent, in acid representing the strength of the gastric juice. The potters found themselves unable to accept this standard, and offered instead a 5 per cent, standard for white and