In making lemon chrome, the tub in which the precipitation is to take place is two-thirds filled with water, the lead solution is stirred in, and then the chromate solution, mixed with the proper quantity of sulphuric acid, is run in; the liquid is well stirred so that the precipitate may form as quickly as possible throughout the whole liquid. The precipitate is allowed to settle, the liquid drawn off, and the colour washed twice with water as quickly as possible. The paste is then removed from the tub and poured on a strong linen strainer. At first, the fine precipitate goes through the strainer, the liquid is poured back on the strainer until the size of its pores is so far diminished by the precipitate itself that only clear liquid runs through. The precipitate is left on the strainer until it forms a stiff mass, which can be easily spread out upon boards by spatulas. To obtain a good, that is, a loose product, it is necessary to carry out the processes so quickly that the swelling mentioned above does not take place while the colour is being strained, but when it has been spread out on the boards. This swelling only takes place completely when the layer of precipitate is fairly thin. Large boards should be used, upon which the precipitate is spread out in a very thin layer. To prevent the mass—which is still fairly fluid—from running off the boards, they are provided with raised edges, and the paste is spread out smoothly in these flat trays. If the operations have been properly performed, the precipitate at once begins to swell and becomes of a loose nature. When it has acquired a buttery consistency it is cut up, by means of a thin sheet of brass, into prisms, which are placed near one another standing on the narrow side, and dried first in the shade and then in the sun. It is necessary that the drying should take place slowly at first, or the cakes will crack or even fall to pieces. The precipitate cannot be washed completely in the tub, because it often begins to swell on the strainers, consequently a crystalline crust covers the surface of the cakes during drying. This layer must be removed by scraping the cakes of colour, in which operation small quantities of chrome yellow dust become suspended in the air. To protect the workman against poisoning by this lead compound, precautions must be taken against breathing in the dust. The simplest and most efficacious is to tie a wet sponge over mouth and nose; this retains the particles of dust in the inspired air. The dust, scraped off the cakes, is put into water, in which the salts dissolve, whilst the chrome yellow sinks to the bottom. In this process for preparing chrome yellow the solution of potassium acetate left after the precipitation contains a considerable quantity of free acetic acid, which may be utilised to dissolve lead.