_Examination of Paper for Loading._--If a piece of paper is crumpled up, placed in a small crucible, and then ignited until all the carbonaceous matter has been burnt off, a residue is left in the crucible which may be white or coloured. This is usually termed the _ash_ of the paper. The amount of ash present is determined by taking a weighed quantity of paper and weighing the residue obtained. Special appliances can be obtained for making rapid determinations of the ash in paper, but for occasional analyses they are not required. _China Clay._--This is the best known and most commonly used loading. The purest form of this material is kaolin, a natural substance formed by the gradual decomposition of felspathic rocks arising from exposure to the long-continued action of air and water. The clay occurs in great abundance in Dorset, Cornwall, and Devon, the southern counties in England, where the most famous deposits are found. The natural mineral is levigated with water, and the mixture allowed to flow through a series of settling ponds, so that the clay gradually settles in the form of a fine deposit. The clay is dried and packed in bags. Its value is controlled largely by the purity of its colour and its freedom from grit and sand. It is essentially a silicate of alumina, having the approximate composition-- Silica (SiO_{2}) 43·00 Alumina (Al_{2}O_{3}) 35·00 Combined water 10·00 Moisture and impurities 12·00 ------ 100·00 The specific gravity of the dry substance is 2·50. It is utilised as a loading in all kinds of paper, and forms also the main ingredient in the coating found on ordinary art and chromo papers. _Ash containing China Clay._--In news, cheap printings, and common art papers the ash almost invariably contains china clay. This substance is insoluble in dilute acids, but is acted upon by concentrated sulphuric acid when digested for some time. A simple test for the presence of china clay in ash is the blue coloration which is obtained when the ash after being ignited is gradually heated with a few drops of solution of cobalt nitrate. China clay can be decomposed by fusion with carbonate of soda in a crucible. By this means silicate of alumina is decomposed, and the alumina goes into solution, the silica remaining as an insoluble residue. The filtered solution is boiled with an excess of ammonia which gives a gelatinous precipitate of aluminium hydrate. _Sulphate of Lime._--This compound is valued chiefly for its brilliancy of colour, being used in high-class papers. It is slightly soluble in water, to the extent of about 23 lbs. in 1,000 gallons, and this fact must be taken into account when the material is added to the pulp in the beating engine.