VOL. LXXXIX.] PHILOSOPHICAL TRANSACTIONS. 52<) 



Scale of Barks. 



Tanning principle, Tanning principle, 



Tanning (in grs.j, from § Tanning (in grs.j , , from § 



Gallic prin- a pint of infusion Gallic prin- a pint of infusion 



acid, by ciple, by and l oz. of solu- acid, by ciple, by and loz. ofsolu- 



colour. hydrometer, tion of glue. colour, hydrometer, tion of glue. 



Bark of Cherry-tree 8 4.2 59 



Elm* 7 2.1 28 Sallow 8 4.6 59 



Oak, cut in the \ „ 01 „r» Mountain ash 8 4.7 60 



winter. S V M ■ J ° Poplar 8 6.0 76 



Horse chesnut. . . 6 2.2 30 Hazel 9 6 3 79 



Beech 7 2.4 31 Ash 10 6.6 82 



Willow (boughs) .8 2.4 31 Spanish chestnut. 10 9.0 98 



Elder 4 3.0 41 Smooth oak 10 9.2 104 



Plum-tree 8 4.0 58 Oak, cut in spring. 10 9.6 108 



Willow (trunk) . . 9 4.0 52 Huntingdon or / 



Sycamore 6 4 1 53 Leicester willow \ 1U * w * 1 luy 



Birch 4 4.1 54 Sumach 14 16.2 158 



It is to be observed, that the barks do not keep any respective proportion in the 

 quantity of gallic acid and tanning principle contained in each; which is an evidence 

 of the distinctness of principle, and may perhaps open a new field for saving oak- 

 bark in dying, as the willows, sallow, ash, and others, produce a very fine black. 

 It is also worthy of observation, that the quantities of gallic acid and tanning prin- 

 ciple do not differ in equal proportions, between the winter and spring felled oaks. 

 This fact may lead to the discrimination of the proper time for cutting; which is 

 probably when the sap has completely filled and dilated that part of the vegetable 

 intended for use. This will make a difference in the season of cutting oak, elm, 

 and other trees, shrubs, &c. Leaves should be taken when arrived at their full 

 size, and then dried under cover; for, as the tanning principle is so soluble, and 

 the substance that contains it so thin, in a leaf, the dew alone might dissolve it. 

 Finally, as the gallic acid does not seem to combine with the matter of skin, and 

 as its astringency will corrugate the surface, we may I think conclude, that its pre- 

 sence in tanning is not only useless, but detrimental. 



XVI. On the Resolution of Algebraic Equations : attempting to distinguish parti- 

 cularly, the Real Principle of every Method, and the True Causes of the Limi- 

 tations to which it is subject. By Giffln Wilson, Esq. p. 265. 



1. The practical management of algebraic equations, as far as respects the 

 solution of problems depending on them, is well understood; but their general 

 theory, being considered as an abstruse and purely speculative subject, is no where, 

 that I have seen, so fully analysed, as with all the assistance to be derived from the 

 application of the principles of combination, it appears it might be. — 2. The diffi- 

 culties under which the higher branches of algebra still labour are generally known. 

 No degree of equations beyond the 2d, is yet perfectly resolved : cubics present 

 frequently an irreducible case: biquadratics have, by several methods, been reduced 



* The infusion of the elm was so loaded with mucilage, that it was with difficulty I could separate 

 the tanning principle, or try the specific gravity. — Orig. 

 YOL. XVIII. 3 Y 



