L. TECHNOLOGY. 481 



ing added to the wool to insure the combination of the great- 

 est strength and greatest fineness. Yet it is said that in Ger- 

 many, especially in Berlin, all the difficulties in the way of 

 spinning this yarn have been overcome, and the fabrics man- 

 ufactured from it there even surpass in strength those made 

 in France. 5 , 1871, 106. 



DETECTION OF SILK IN FABRICS. 



According to Mr. Spiller, silk can always be identified in a 

 mixture with any other animal or vegetable fibre by means 

 of concentrated hydrochloric acid, which dissolves it com- 

 pletely and immediately without appreciably affecting any 

 woolen or woody fibre with which the silk may have been 

 interwoven. Strong sulphuric acid has also a powerful solv- 

 ent effect upon silk, and is likewise much more destructive in 

 its action upon cotton than the other acid. Should it be de- 

 sired to determine the nature of any fibres remaining after 

 the solution of the silk, it is first necessary to wash and col- 

 lect them, when they will usually be found destitute of color. 

 To decide whether wool is present or absent, a solution of 

 picric acid may be employed, which instantly imparts a full 

 yellow tint to the wool, but does not in the least affect cotton, 

 linen, or China grass, so that it is only necessary to immerse 

 the fabric in the dye, wring it out, and wash well with water. 

 Should any portion remain of a yellow color, the presence of 

 wool is indicated. Other methods can be employed similar 

 in principle, but the picric acid is believed to be best. Dis- 

 crimination between the different kinds of woody fibre can 

 best be prosecuted by means of the microscope. 18-4, Octo- 

 ber 21,102. 



PEARL IIARDENEFt. 



A substance known as pearl hardener, introduced a few 

 years ago for the purpose of hardening paper, is prepared by 

 precipitating hydrated sulphate of lime from a perfectly pure 

 solution of chloride of calcium, by means of sulphuric acid. 

 Great care is taken in its preparation, and it is coming rap- 

 idly into use for the purpose of increasing the weight and 

 density of paper pulp. At the present time it is said about 

 3000 tons are made annually in a single town in England. 

 17 A, December, 186. 



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