MICROSCOPE IN MANUFACTURES 



pillar is called, consists of three layers, an outer 

 layer of floss, a middle layer and a so-called layer 

 (the inner layer) of parchment. Only the middle 

 layer is used in commerce, the floss is too fine and 

 weak and the parchment is so impregnated with 

 i silk glue as to be useless. 



If we examine some raw silk, taken from the 

 middle layer of a cocoon, we can easily see the two 

 parallel fibres of silk and the outer wrinkled cover- 

 ing of silk glue. Now, magnifying our object more 

 highly, we shall see that each fibre is a solid rod, 

 with a smooth lustrous surface and without any 

 sign of lumen or cell structure; the rods too are 

 continuous and this alone distinguishes silk from 

 all other fibres animal or vegetable. Two tests are 

 worth trying for they are characteristic of silk. On 

 the addition of a little strong sulphuric acid we 

 observe that the silk rapidly dissolves, on the other 

 hand, if a few fibres are boiled in hydrochloric 

 acid, the silk dissolves but the envelope of silk glue 

 remains unchanged and appears beneath the micro- 

 scope as a cracked and wrinkled tube. 



The caterpillar of another moth spins coarser 

 greyish coloured fibres, which are spun into the 

 well known Tussore silk. As with the common 

 silkworm these caterpillars spin two fibres and glue 

 them together with silk glue. In this case, how- 

 ever, under a high magnification we shall notice 

 that the fibres are marked with a number of very 

 fine lines running lengthways, whilst every now 

 and then there are fairly deep indentations. The 



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