It is indeed the practical nature of the alchemical doctrine taught in the _Liber Luminis_ which strikes us most strongly when we read this book. A large part of it is taken up with exact descriptions of the minerals, according to their various forms and the countries from which they were derived. The rest consists of receipts for their employment in refining metals. Whatever we may think of the validity and use of these processes, we cannot fail to notice that they are described in a perfectly straightforward and simple style. Here are none of the mysteries, the riddles and ridiculous allegories so common in chemical works written at a later time. The truth of the matter may probably be that, in following the doctrine here set forth, Michael Scot and the alchemists of his time did obtain results which were then so surprising, as to excuse a certain exaggeration in those who described them. Tests that could touch and reveal the real nature of the metals under any change of outward appearance were not then so well known as now. Copper that had been made to shine like gold, or to assume the appearance of silver, was practically gold or silver to those who had no means of discovering that the real nature of the metal itself remained unchanged. Thus then are to be understood the assertions of the _Liber Luminis_ regarding transmutation. They are plainly made in all good faith, and depend on the doctrine already mentioned, which held that the differences between the metals were an affair of the superficial form rather than of the underlying substance. To change the appearance of one metal to that of another, was therefore to effect a real transmutation: the only one conceivable by the philosophers of that time. When the _Liber Luminis_ speaks of giving copper ‘a good colour,’ or preparing iron to ‘receive the appearance (_formam_) of silver,’ these expressions reveal with frank sincerity the conceptions of this alchemy and the results it endeavoured to obtain.