In this process, the temperature at which the operation commences is important. The cooler the mixture which is placed in the flasks before shaking, the paler will be the colour of the vermilion obtained. It is to be supposed that the reaction, which is but slow in the cold, forms in consequence of its slowness a black sulphide of such character that in its subsequent transformation into the red crystalline sulphide very small crystals are produced. The Gautier-Bouchart method for the preparation of vermilion from mercury and ammonium sulphide is applied on the large scale as follows: 1,000 parts of mercury are shaken for 7 hours with 200 parts of flowers of sulphur and 400 parts of ammonium sulphide saturated with sulphur; the dark-coloured mixture is exposed for several days to a temperature of 60° C., when the colour changes to red. In addition to the usual washings, the mass is further treated with nitric acid. The purpose of this operation is to oxidise all the free sulphur to sulphuric acid. For a colour works in which, in addition to vermilion, are made other pigments, especially such as are sensitive to the action of sulphuretted hydrogen, this process, which produces vermilion of a good shade, although not particularly stable, is not to be recommended on account of the evolution of sulphuretted hydrogen, which cannot be completely prevented even by the greatest care. =Liebig’s Process.=—The starting point in the manufacture of vermilion by this process is the compound known as white precipitate (see below). It is only necessary to heat white precipitate with a solution of ammonium sulphide saturated with sulphur, at 40° to 50° C., for a long time. The operation may be conducted in well-closed flasks in a place the temperature of which is, as nearly as possible, 45° to 50° C., such as the flues leading from a furnace in constant use. The change of colour is gradual; this is an advantage, since it is easier to obtain the correct shade. By treating the product with weak caustic potash solution it may be made still brighter. After washing and drying at a gentle heat the pigment is finished. This method is especially adapted for manufacturers not exclusively engaged in making vermilion. No special arrangement of apparatus is necessary; the apparatus for making ammonium sulphide and a number of glass flasks are the only essentials. There is another considerable advantage, that the product cannot be completely spoiled. The process of formation of the vermilion is tolerably slow; a careful observation of the progress of the earlier operations is sufficient to determine the time required. In order to be able to do this with certainty, it is necessary to work always under exactly the same conditions; the same quantity of white precipitate must always be used and the solution of ammonium sulphide must always have the same strength.