Wo. 2.] 



OF AGRICULTURE, SCIENCE, AND ART 



EDITED BY D. PEIRCE. 



Pliila<lcl|»lii:i, Moiii€l:)y, IVovcinbt^r 5, 1S3§. 



[Vol. I. 



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SILK WORM AND SILK MANUFACTURE. 



The caterpillar or larva, emphatically 

 known by the title of the silk worm, is, 

 when full grown, nearly tiiree inches long 

 and of a yellowish gray colour; on the 

 upper part of the last joint of the body 

 is a horn-like process, as in many of the 

 spinges. It feeds, as every one knows, 

 on the leaves of the white mulberry, in 

 defect of which may be substituted the 

 black mulberry, and even in soine instan- 

 ces, the lettuce and a few other plants. 

 The silk worm remains in its larva state 

 about six weeks, changing its skin four 

 times during that period, and, like other 

 caterpillars, abstaining from food for some 

 time before each change. When full grown 

 the animal entirely ceases to feed, and 

 begins to form itself a loose envelopment 

 of silken fibres in some convenient spot, 

 which it has chosen for that purpose; and 

 afterwards proceeds to enwrap itself in a 

 much closer covering, forming an oval 

 yellow silken case or ball, about the size 

 of a pigeon's egg, in which it change? to 

 a chrysalis, and after lying thus enclosed 

 for about the space of fifteen days, gives 

 birth to the moth. — This however is al- 

 ways prevented when the animals are 

 reared for the purpose of commerce; the 

 moth greatly injuring the silk of the ball 

 by discharging a quantity of coloured fluid 

 ■ before it leaves (he cell; the silk-balls are 

 therefore exposed to such a degree of heat 

 as to kill the enclosed chrysalides, a fevv 

 only being saved for the breed of the fol- 

 lowing year. The moth, when hatched j 



is a short-lived animal, breeding soon af- 

 ter its exclusion; and when the females 

 have laid their eggs, they, as well as the 

 males, survive but a very short time. 



The length of the silken fibre or thread 

 drawn by the silk-worm may be supposed 

 to differ considerably in different silkl)alls. 

 According to Boyle, as quoted by Dur- 

 ham, a lady, on making the experiment, 

 found the length of the ball to be consid- 

 erably more than 300 yards, though the 

 weight was only two grains and a half. 



The Abbe La Pluche informs us, that of 

 two balls, one measured 924 feet, and the 

 other 930. It may be proper to add that 

 the silk throughout its v/hole length is 

 double or composed of two conjoined or 

 agrahitinated filaments. 



Silk as spun by the animal, is in the 

 state of fine threads, varying in colour 

 from white to a reddish yellow. It is 

 very elastic, and has considerable strength 

 if we consider its small diameter. It is 

 covered with a varnish, to which its elas- 

 ticity is owing. This varnish is soluble 

 in boiling wafer; but alcohol does not act 

 upon it. Hence it has been compared to 

 a gum, though it approaches much nearer 

 to a gelatine; since BerthoUet has shown 

 that it is precipitated by Tan, and by Mu- 

 riate of Tin. It differs however, from 

 gelatine in several particulars. Alum 

 throvvs it down of a dirty white; Sulphate 

 of Copper, of a dark brown, and Sul- 

 phate of Iron, of a brown colour. 



When the water is evaporated, the var- 

 nish is obtained of a black colour, brittle, 



