In a colour works in which many pigments are made sulphuretted hydrogen is frequently required. Since all lead pigments are blackened by this gas, the greatest care is required in using it. Also the poisonous nature of sulphuretted hydrogen is generally under-estimated. In working with sulphuretted hydrogen, the apparatus depicted in Fig. 3 should be used. It should be placed in a position, such as a closed yard, in which escaping gas will be harmless. If this cannot be done the precipitation should be accomplished in closed vessels, from which a pipe should carry the gas to a fire, where it will be burnt to sulphur dioxide and water. In most cases the manufacturer of colours makes but a certain number of pigments and rarely or never all which are mentioned in his price lists. The dimensions of the establishment will be in accordance. In commencing a new colour works it is advisable from purely financial reasons to produce at first a limited number of colours, but these in perfection. By many experiments and diligent study of chemistry a colour manufacturer may hope to compete successfully in so difficult a branch of chemical technology as the manufacture of colours. CHAPTER LXXIV. COMMERCIAL NAMES OF PIGMENTS. In commerce the pigments are found under the most different names, the most common of which have been given together with the description of the pigment. No regularity can be found in the names chosen for the different pigments; quite arbitrary designations have been taken. Pigments are most commonly named after places—for example, Prussian blue, Paris blue, Bremen green; also after the discoverer—Turnbull’s blue, Hatchett brown. Whilst these names give the place of production or the name of the discoverer, and thus have some foundation, there are many others for which no reason can be assigned, _e.g._, King’s yellow. Certain names are based upon the chemical composition of the pigment. These should be used by preference, but now that the expressions white lead, chrome yellow and Chinese blue have become common no one would think of speaking of basic lead carbonate, lead chromate or ferric ferrocyanide. The confusion in the nomenclature of colours is increased by placing pigments which possess English names upon the market under French, German or Latin names, which are often sadly mutilated. This is more the case in Germany than in England. It may easily happen that a reader of a work on colour making might search in vain for a pigment whose name he had somewhere heard, whilst the book contained a description of the colour and its properties, but under another name. To remove this difficulty it has been thought necessary to collect the names of the different pigments, which are contained in the following table. The French and German names are also given. The most usual names are printed in italics. WHITE PIGMENTS.