Page:Proceedings of the Royal Society of London Vol 1.djvu/214

Rh tions of Mr. Biggin and Mr. Davy, which show that the proportion of tan in the same trees is different at different seasons, and that it is principally contained in the white interior bark, which bark is ' comparatively most abundant in young trees, he observes, that there seems to be an intimate connexion betWeen the formation of new Wood and the formation of tall, in those vegetables which afford the latt ; and thinks it very probable that such vegetables have the facul y of absorbing more carbon and oxygen than is required in the formation of the vegetable principles, especially of the woody ﬁbre ; and that this excess of carbon and oxygen, by chemical com- bination, becomes tan, which is secreted in the white interior bark, and afterwards decomposed, and employed in the formation of the new wood.

The ligneous substance of vegetables, Mr. Hatchett says, appears to be composed of carbon, oxygen, hydrogen, and nitrogen ; and he has reason to think, from some synthetical experiments he has made, that tan consists of 53 parts of pure carbon, and 47 of oxygen.

In the concluding section, Mr. Hatchett observes, that the whole of the present paper may be concentrated into one simple fact. namely, that tan is composed (at least essentially) of carbon and oxygen; and that, although it has hitherto been deemed a peculiar principle, formed by nature in certain vegetables, it may, with the gr'éatest ease, be produced, by presenting oxygen to carbon in the humid way, under the circumstances which have been described.

Since the experiments which have been related were made, Mr. Hatchett has, he says, further proved the efﬁcacy of the factitious tan by actual practice; as he has converted skins into leather by means of tan produced from materials which, to professional men, must appear extraordinary, such as deal sawdust, asphaltum, turpen- tine, pit-coal, wax candle, and a piece of the same sort of skin. Allowing, therefore, that the artiﬁcial production of tan must for the present be principally regarded only as a. curious chemical fact, not altogether unimportant, yet, as the principle on which it is founded has been developed, we may, Mr. Hatchett thinks, hope that a more economical procs will be discovered, so that every tanner may be enabled to prepare his tan, even from the refuse of his present ma- terials.

The woman whose case is here described was born in Radnorshire in the year 1770. She was of a fair complexion, and, except when irritated, of a mild temper. In her diet she was remarkably abstemious, eating very little, either of animal or vegetable food; and if at any time she ate a hearty meal, or took several kinds of food, she was so much affected by it as to faint. She was of a costive habit,