By admixture with white, cadmium gives a series of beautiful clear tints. When compounded with white lead, however, the colour has been stated to be destroyed. Theoretically, this might very well happen. Cadmium yellow is composed of cadmium and sulphur--white lead of lead and carbonic acid. If the former parted with some of its sulphur to the latter, sulphide of lead would result, which is black. Hence, the partly decomposed yellow and white would be mixed with black, and there would be formed a blackish-yellow or a yellowish-black. Again, if the cadmium parted with the whole of its sulphur to the lead, receiving in exchange the carbonic acid of the latter, a mixture of black sulphide of lead with white carbonate of cadmium would be furnished, the result being a grey. Perhaps the following rough diagram may serve to make our meaning plainer:-- Cadmium Yellow {Cadmium. __________ Carbonate of Cadmium (White.) {Sulphur. / \ / \ / \ / \ / \ / \/ /\ ____/__\ White Lead {Lead. / Sulphide of Lead (Black.) {Carbonic Acid. Such is the theory of the reaction which might take place, but which, as far as our own experience goes, does not. Some deep cadmium yellow which we ourselves prepared was intimately mixed and ground with an equal quantity by weight of Cremnitz white, and an oil rub of the compound laid upon a tile. Having placed the latter on a shelf in the laboratory, we watched from week to week to see if any approach to blackness occurred, any diminution in the beauty of the tint; but could perceive none. Hence, while admitting the possibility of the colour being damaged or destroyed in the case of an inferior and spurious article, we conclude that an unadulterated cadmium yellow, containing no free sulphur, neither injures, nor is injured by, white lead, and may safely be used therewith. At the same time, the artist should be warned to satisfy himself of the genuineness of his pigment, or otherwise to employ the white of zinc, at least as a medium of intervention. A good sample of cadmium yellow may rather advantageously than otherwise be compounded with white lead, for we have found that a mixture of equal parts by weight of the two will bear an atmosphere of sulphuretted hydrogen that completely blackens the white alone. With all the sulphides of cadmium a steel palette knife is best avoided. 22. PALE CADMIUM.