SIR H. DAVY S AGRICULTURAL CHEMISTRY. 



179 



the mean proportioli of vvater being ^5 

 or 30 times the weight of the silk. 



Comparative experiments being made, 

 the white raw silk, prepared with soap, 

 was very white and brilliant, with soda 

 soft, but less white, as having a yellowish- 

 gray tinge; with water, although very 

 soft, dull, and having a yellowish-gray 

 tinge. Yellow raw silk exhibited the 

 same differences, but the soda had not 

 acted so strongly upon it as the water. 



The white siiks lost upon an average 

 24 to 25 per cent, and the yellow 26 to 

 28. The silks prepared with soap were 

 stronger than those boiled in water, or 

 with soda; and were of superior bril- 

 liancy when dried. In boiling silk, cop- 

 per vessels have some inconveniences. 

 Oil account of the ease with which they 

 are oxidized: and as calcareous salts pre- 

 sent in the water diminish the soap, it is 

 necessary to use very pure water, and 

 only a certain quantity, which is 15 or 

 16 times the weight of the silk: .^^2'^^ ^^ 

 Ith of soap is sufficient for white raw 

 silk; but for yellow raw silk, it is neces- 

 sary to add 50 or 60 per cent, of soap. 

 Even an equal weight of soap, and the 

 subsequent use of sulphurous acid gas, 

 does not render these silks as white as 

 the other, when treated with 25 per cent, 

 of soap.. As to the time of boiling, the 

 silk which was boiled the least time was 

 whiter, more brilliant, and had lost less 

 of its weight than that which had boiled 

 a longer time. 



Silk, if the boiling be continued too 

 long, loses the white color it has acquir- 

 ed; the following experiments, were 

 made to determine the cause of this al- 

 teration; white raw silk, boiled in a ves- 

 sel which permitted |tbs of the water to 

 be evaporated, was not so white as that 

 boiled in a vessel that did not permit 

 any evaporation to take place. 



Very white silk, which had been boil- 

 ed with soap, was again boiled for an 

 hour in soap-liquor and in solution of 

 gum; it acquired a reddish tint, that 

 could not be got rid of by boiling water. 



Silk, already bleached by soap, was 

 boiled again for four hours, with a quar- 

 ter its weight of soap. The white silk, 

 thus doubly bleached, had a greenish-gray 

 tint; it was dull and harsh, having ac- 



quired some resemblance to thread in 

 hardness; it had lost -j^'^ of its weight, 

 and 7 per cent, of its strength. 



The yellow raw silk, was whiter than 

 at the first bleaching, but had lost some 

 of its softness and brillancy, with j^yth 

 of its weight, and 5 or 6 per cent, of its 

 strength. 



White raw silk, bleached by soap, and 

 very white, being boiled, after careful 

 washing, for many hours in distilled 

 water, and the water afterwards evapo- 

 rated, yielded a small quantity of animal 

 matter, not analogous to the products 

 above spoken of, but which burned in 

 the same manner as silk. 



As silk is completely bleached in less 

 than an hour, the boiling should not ex- 

 ceed that time; the soap and silk being 

 put in about half an hour before the water 

 boils, and the silk frequently turned. A 

 less time would suffice for trames and or- 

 gan zines. 



It is to the alterations which take place 

 when the boiling is too long continued, 

 that the impossibility of aluming silk in 

 the hot bath is owing; and the loss of 

 brilliancy when silk is dyed of colors 

 rather brown, for which a boiling heat is 

 necessar}'. — t/iiui. de C/iim. Vol. 65. 



SIR H. DAVY S AGRICULTURAL CHEMISTRY. 

 (Conliiiutd from p. 164.) 



To ascertain the primary elements of 

 the different vegetable principles, and 

 the proportions in which they are com- 

 bined, different methods of anal)'sis have 

 been adopted. The most simple are 

 their decomposition by heat, or their 

 formation into new products by combus- 

 tion. 



When any vegetable principle is acted 

 on by a strong red heat, its elements be- 

 come newly arranged. Such of them as 

 are volatile are expelled in the gaseous 

 form; and are either condensed as fluids, 

 or remain permanently elastic. The fix- 

 ed remainder is either carbonaceous, 

 earthy, saline, alkaline, or metallic matter. 



To make correct experiments on the 

 decomposition of vegetable substances by 

 heat, requires a complicated apparatus, 

 much time and labor," and all the re- 

 sources of the philosophical chemist; but 



