106 farmers' AAiD MKCHANICS' JOURNAL. 



their bases rounded, to burnish those pieces which are concave or 

 rinsi-shaped. 



The burnishing of the edges of books, is performed with a wolf's 

 or dog's tooth, or a steel burnisher : for this purpose, they place 

 the !)ooks in a screw-press, with boards on each side of them, and 

 other boards distributed between each volume •, they first rub the 

 edges well with the tooth, to give them a lustre. After sprinkling 

 or staining, and when the edges are become dry. they first burnish 

 tliC tVont ; then turning the press, they burnish the edges ai the 

 top and bottom of the volume. 



They burnish the gilt edges in the same manner, after having 

 applied the gold ; but observe, in gilding, to lay the gold first upon 

 the front, and allow it to dry ; and, on no account, to commence 

 burnishing till it is quite dry. [Diet. Technologique. 



ON DYING WITH PRUSSIAN BLUE. 



A NEW method of dying with Prussian Blue has been discovered 

 by Prof. Raymond, of Lyons. By this process it is said, " that a 

 brilliant and permanent color is produced ; more bright, and equal- 

 ly deep, with those obtained from indigo, whilst it will also furnish 

 a sky-blue, not attainable from that substance, which is likewise 

 more costly. 



To dye silk of a Raymond blue, it is to be cleansed in a large 

 quantity of water, after the usual boiling with soap ; it is then to 

 be immersed in a solution of persulphate of iron, (that is, of that 

 kind of copperas, which is of a dark green color,) the oxide of which 

 will combine with the silk ; the greater or less intensity of the 

 shade of yellow which the silk acquires, will furnish the means of 

 judging when a proper quantity of the ferruginous solution has been 

 absorbed ; after which it is to be rinsed with great care, to remove 

 all the free acid ; the silk is then to be immersed in a bath of prus- 

 siate of potash, acidulated by sulphuric acid. In a few minutes 

 the dying will be completed ; when this is effected, it must be rins- 

 ed in clear water, and brightened with purified urine, diluted with 

 a largo portion of water, into which is occasionally thrown a small 

 portion of acetic acid, to guard against a too powerful action of 

 the alkali. 



The only difficulty which has yet been experienced in dying 

 with Prussian blue, has been to obtain, at will, a regular gradation 

 of shades, between the most intense blue and a perfect white. M. 

 Raymond, Jun., has sent to the Society for the encouragement of 

 Arts, [in France,] patterns of every shade obtainable from indigo; 

 but it has not yet been proved that the process is applicable in the 

 large way. 



M. Chevreul has recently read to the Institute, a memoir upon 

 a process remarkable for its simplicity, by which he has lately ob- 

 tained a perfect gradation in the shades of color dyed by Prussian 

 blue, which are at the same time, more permanent and more beau- 



