The kaolin alluded to in the first column is a remarkably pure material, perfectly white, and contains an enormous quantity of water. It refers to one of the finest washed china-clays in the market, and is extensively used in porcelain manufacture. It is quoted here principally to give an idea of what a really pure clay is like chemically. We notice that, in spite of its relative purity, it contains .27 per cent. of iron oxide. This could have been well done without, from the manufacturer’s standpoint, but is of course a very minute proportion. Small as it is, it must exert a slight amount of colouring influence. The lime and magnesia are present in slightly larger proportions, and a little more of either would be advantageous rather than otherwise, as assisting to flux the material. This is an earth with which practically anything may be done by judicious blending and careful preparation. With reference to the second column, the figures do not refer to any particular clay, but they have been compiled to show the average composition of kaolins as used in the market. It will be observed that the silica and alumina are present in approximately equal proportions, which is a characteristic of fairly good china-clays. The iron oxide remains as before, but there is a larger proportion of lime and magnesia--as much as can be permitted except in a second-rate clay. The evidence of the third column shows that the sand in the china-clay is to a large extent quartzose, and this is at the expense of the alumina. Such a material would be suitable for making a species of white fire-brick, and it might do for the commoner kinds of china-ware. The earth is really of the nature of a loam--a sandy clay. There is too much iron in it for the production of perfectly white goods. The proportion of lime might be increased to advantage. _Chemical Composition of Fire-clays from Newcastle-on-Tyne._[9] ------------+-------+-------+-------+-------+-------+-------+-------- | 1 | 2 | 3 | 4 | 5 | 6 | 7 +-------+-------+-------+-------+-------+-------+-------- Silica | 51.10 | 47.55 | 48.55 | 51.11 | 71.28 | 83.29 | 69.25 Alumina | 31.35 | 29.50 | 30.25 | 30.40 | 17.75 | 8.10 | 17.90 Iron oxide | 4.63 | 9.13 | 4.06 | 4.91 |} 2.43 | 1.88 | 2.97 Lime | 1.46 | 1.34 | 1.66 | 1.76 |} | |} 1.30 Magnesia | 1.54 | .71 | 1.91 | trace | 2.30 | 2.99 |} Water, etc. | 10.47 | 12.01 | 10.67 | 12.29 | 6.94 | 3.64 | 7.58 ------------+-------+-------+-------+-------+-------+-------+--------