A new loading material called “agalite” has been lately introduced, possessing certain advantages over china clay, {134} or calcium sulphate. Agalite is a mineral of the nature and chemical properties of asbestos: it consists of nearly pure magnesium silicate. Its structure is more or less fibrous, like that of asbestos, which, as is well known, can be spun and woven and even made into paper, and it therefore, when added to a paper, forms a part of the fabric itself. It is even claimed that it assists in keeping back some of the finer fibres that invariably find their way through the meshes of the wire cloth, and it is said that 90 per cent. of the amount added to the engine is found in the paper. In the case of china clay it is well known that only from 40 to 60 per cent. is actually “carried” by the pulp. Figs. 40, 41, 42, and 43 show the appearance of china clay, pearl-hardening, and agalite when viewed under the microscope, magnified 200 times. The nature of agalite is such that it assists the paper in taking a high finish. This is probably due to its “soapy” nature, a feature which is characteristic of asbestos, French chalk, “soap-stone,” and other magnesium silicates. [Illustration: FIG. 44.] When papers contain such excessive quantities as 15 or 20 per cent. of clay, it cannot be to the advantage of the consumer, and should be looked upon as an adulteration. It is a matter of some importance to be able to determine rapidly and accurately the amount of mineral matter in a paper. The usual method is to ignite a weighed quantity of the paper in a platinum crucible until the ash so obtained is either white or a very pale grey. From the weight of the ash, the percentage of mineral matter is easily calculated. The following is a very convenient plan in cases where a platinum crucible or dish is not obtainable:—Take a weighed piece of the paper to be examined, from 2 to 4 in. square, according to the thickness, roll it into a narrow hollow cylinder. Round this wind a weighed piece of platinum wire about 1⁠/⁠50 in. thick, as in Fig. 44. Hold this by means of a pair of crucible tongs in the flame of a Bunsen burner until it is completely burned. If the wire is carefully wound round, and especially if the roll of paper is made conical, the ash will be securely held in {135} position. Those who do not possess a chemical balance of the ordinary form will find a convenient substitute, which will answer the purpose of weighing the paper and ash with sufficient accuracy, in the spiral balance invented by Prof. Jolly[11] illustrated in Fig. 44. It consists of a spiral of hard wire A, which is suspended in front of a mirror B, upon which millimetre divisions are marked. A small float D, dipping under the surface of the water in the vessel E, is provided for the purpose of steadying the spiral and allowing it to come quickly to rest. The balance is provided with a light pan made of a thin plate of mica, and suspended by very thin platinum wires.