The results of a chemical analysis of a compound earth, as ordinarily used by the brickmaker, widely differ from those obtained by a mineralogical or petrological examination. The petrologist views the earth as a mineral aggregate, the constituents of which may be ascertained on appeal to a properly-constructed microscope--that is, in the majority of instances. By noting the relative proportions of the different minerals, he is enabled to state, with approximate accuracy, what is the ultimate chemical composition of the whole. From this it would appear that a rough chemical analysis could be drawn up by the petrologist without having recourse to the ordinary methods of chemical investigation. And in a limited sense that is true. But we should not lose sight of the fact that there is, in too many cases, an amorphous residuum in earths, the nature whereof the microscope is powerless to reveal. It is upon this remnant that the chemist should direct his most careful attention. The mineralogist also can give a shrewd idea of the chemical composition of a brick-earth by using a blowpipe and accessories. This, in fact, may be regarded as a chemical means of investigation; but it possesses this serious drawback, viz., the blowpipe only yields a qualitative, and not a quantitative analysis. In other words, it can tell us something concerning chemical compounds present in an earth, but rarely informs us as to the relative proportions of them. Even this, however, is of great service in many instances, though it does not possess the value of a quantitative analysis. For example, we have stated previously that certain ingredients are very undesirable in a brick-earth, even in minute quantities; and that fact becomes of increased value if we extend the field to earths used in terra-cotta, and china and porcelain manufacture. Now, the blowpipe is a handy instrument; it may be carried about by the prospector with its usual accessories, and occupies but little space. Suppose he discovers a bed of white earth which he believes to be good china-clay; he can prove that fact, or at least obtain a great deal of information to that end, by the mere use of that useful little instrument. Knowing, for example, that fluorine is an undesirable constituent in such a clay for many high-class purposes, he might test first of all for that; iron, perhaps, may come next, and so in a few minutes he is enabled to arrive at some valuable particulars that would take much longer to obtain by chemistry in the wet way.