CHEMICAL SCIENCE. 255 



become brittle. Some descriptions of leather, on the other hand, be- 

 come converted into a mass somewhat resembling glue. When Prel- 

 ler's leather is tried in the same way, it gradually approaches to the 

 condition of horn, but it requires several hours before that state is at- 

 tained. 



We have little more to add to our account of this singular process 

 and its results. Its thinness, pliability and strength, render it imme- 

 diately available for a number of new purposes. Thus by simple twist- 

 ing, it forms an admirable material for " lacings," the strips with which 

 the stitches of the compound driving-band are made. By cementing 

 two or three strips together into a triple thickness, and then paring 

 the edges down to a circular form, an excellent lathe-band is produced 

 which is free from the tendency to become dry and stringy which is 

 now observed in catgut bands. The " but," or lower part of the horse- 

 hide, which on account of its greater thickness, has usually been cut 

 out and applied to separate purposes, is in this process found to be 

 produced in so supple a state, that with a little paring down it may 

 take part equally with the rest of the skin in any purpose to which it 

 is applied. Thus a very large horse-skin is produced, which is ex- 

 tremely valuable for many useful purposes, especially for the cover- 

 ings of carriages. There are several other purposes to which this 

 leather has been applied : but we have said enough to indicate its gen- 

 eral nature and incidents, and the circumstances in which its use 

 would be attended with practical advantage. These are becoming 

 rapidly known and appreciated, and it is not too much to say that Mr. 

 Preller has introduced into this department of industry, a change 

 which will prove as beneficial to the community, as, in a practical 

 point of view, it has already shown itself advantageous, by improving 

 the character of a most useful mechanical appliance. London Meek. 

 Jour. 



OX THE EMPLOYMENT OF PICRIC ACID FOR DISTINGUISHING 

 VEGETABLE AND ANIMAL FIBERS IN STUFFS. 



Dr. Pohl employs a solution of picric acid in water or alcohol for 

 the distinction of vegetable from animal fiber. The original watery 

 solution is diluted with 6 parts, the alcohol with 15-20 parts of water; 

 a small piece of the stuff to be examined is then dipped in the solution. 

 In from 6 to 10 minutes at ordinary temperatures, or in 2 or 3 

 minutes when the fluid is heated to 104 F. the stuff or yarn is taken 

 out and washed with water. Stuffs made entirely of cotton or linen 

 appear perfectly white after washing; but those consisting of wool, 

 or silk, or other animal fibers, acquire a yellow-color, it being under- 

 stood that undyed stuffs are to be used in the experiment. In mixed 

 stuffs the animal fibers appear colored, whilst the vegetable fibers 

 remain white. The test is so exact, that even in those stuffs or yarns 

 in which the individual threads consist of both substances., the pro- 

 portion of animal or vegetable fiber can be exactly ascertained by 

 means of a lens. By the employment of an ordinary thread counter, 



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