Here we have two clays with the carbonates of lime and magnesia present, in one case of over 35 per cent., and in the other of over 26 per cent. Professor Lunge, of Zurich, states that the bricks made from them, if burned at the ordinary heat, say a moderate red heat, are _red_, and do not keep in the air, but crumble away very soon, as the quicklime slackens on combining with the moisture. When burned at a bright red heat, about 200° C. above the former, however, they become nearly white. The lime is then present as a ferri-alumina-calcic silicate, which causes the red colour of the iron oxide to disappear, and, at the same time, entirely prevents any action of the moisture, quicklime being no longer present. We have no hesitation whatever in saying that most British makers would look down upon raw earths such as these from Zurich, and yet many millions of really good bricks have been made from them during the past twenty years, and they are especially noted for their durability. The crux of the case is the temperature at which the earths are burned, as the reader has perceived. Under the heading of “magnesia,” we have said a few words regarding basic bricks. In this country they have been made primarily from magnesian limestone, the chemical composition of which is shown in the following results of analyses:-- _Chemical Composition of Magnesian Limestones._ ----------------------+------+-------+------+------- | 1 | 2 | 3 | 4 ----------------------+------+-------+------+------- Silica | 3.6 | 2.53 | .8 | -- Carbonate of lime | 51.1 | 54.19 | 57.5 | 55.7 „ „ magnesia | 40.2 | 41.37 | 39.4 | 41.6 Iron, alumina | 1.8 | .30 | .7 | .4 Water, &c. | 3.3 | 1.61 | 1.6 | 2.3 ----------------------+------+-------+------+------- _Analysis No. 1_ refers to the well-known magnesian limestone of Bolsover. _Analysis No. 2_ to that from Huddlestone. _Analysis No. 3_ to that from Roach Abbey. _Analysis No. 4_ to that from Park Nook. These results were obtained by Professors Daniell and Wheatstone in connexion with an enquiry many years ago as to the kind of stone suitable for the erection of the Houses of Parliament.