In the wet method there is this essential difference, that it is sought to precipitate the blue and yellow colours upon the inert base by bringing about certain reactions, and therefore while the base remains the same as in the dry method, the colouring media are totally distinct, consisting of lead acetate, bichromate of potash, sulphate of iron, and yellow or red prussiate of potash. The chief condition to be observed with regard to the lead acetate is that it shall be in the proportion of slightly more than three to one of the bichromate of potash; in other words, the bichromate should be a trifle less than one-third the weight of the lead acetate. As to the iron salt, if commercial acetate or nitrate of iron could be bought of constant quality or purity, that would be the most convenient form; but failing that, recourse is had to freshly made and good quality sulphate of iron (green copperas). It is found that the best results are secured when the weight of the sulphate of iron is exactly the same as that of the prussiate of potash. On the score of economy, the yellow prussiate of potash (ferrocyanide) is employed, but the red prussiate (ferricyanide of potassium) gives better and more certain results, and should be adopted when making a superior paint which will command a higher price. As to the comparative merits of the wet and dry systems of mixing the ingredients of Brunswick greens, preference must be given to the former on the score of quality of the pigment produced, but on the other hand it entails much more trouble and skill, and there never can be the same degree of control over the conduct of the operation or the shade of colour developed. The dry method, however, though much more easily carried out, and enabling the exact shade desired to be obtained to a nicety by adding a little more of either the blue or the yellow during the process of manufacture, is seldom adopted, because the quality and fineness of the tints thus secured are much inferior.