Whenever an alkali is employed, it is of the greatest importance that the wood should afterwards be thoroughly washed several times with clean water, in order to remove every trace of the solvents. Any soda or potash remaining in the pores of the wood would not only retain moisture and cause blistering, but would also have an injurious action upon the vehicle of the paint subsequently applied, and in many cases upon the pigment itself. The remarks already made as to the necessity of an absolutely dry surface should be borne in mind in this instance. When the surface of the paint is to be protected by a coat of varnish, the latter should not be applied until the whole of the oil contained in the paint has solidified. The wrinkling of varnish upon paint is frequently erroneously attributed to the bad quality of the varnish, when the real cause is the incomplete oxidation of the paint itself. _Priming._--The first coat of paint applied to any surface is termed the “priming-coat.” It usually consists of red lead and boiled and raw linseed-oil. Experience has shown that such a priming not only dries quickly itself, but also accelerates the drying of the next coat. The latter action must be attributed to the oxygen contained in the red lead, only a small portion of which is absorbed by the oil with which it is mixed. Kali, of Heidelberg, prepares a substitute for boiled oil by mixing 10 parts whipped blood, just as it is furnished from the slaughter-houses, with 1 part of air-slaked lime sifted into it through a fine sieve. The two are well mixed and left standing for 24 hours. The dirty portion that collects on top is taken off, and the solid portion is broken loose from the lime at the bottom; the latter is stirred up with water, left to settle, and the water is poured off after the lime has settled. The clear liquid is well mixed up with the solid substance before mentioned. This mass is left standing for 10 or 12 days, after which a solution of potash permanganate is added, which decolorises it and prevents putrefaction. Finally the mixture is stirred up, diluted with more water to give it the consistence of very thin size, filtered, a few drops of oil of lavender are added, and the preparation is preserved in closed vessels. It is said to keep a long time without change. A single coat of this liquid will suffice to prepare wood or paper, as well as lime or hard plaster walls, for painting with oil colours. This substance is cheaper than linseed oil, and closes the pores of the surface so perfectly that it takes much less paint to cover it than when primed with oil.