ON VEGETABLE MUCILAGES. c35 



some time became opake; but as thisi effect is produced 

 merely by adding it to water, when exposed to the atmos- 

 phere, I was inclined to suppose, that the effect was produced 

 independently of the sugar. . , .- 



These bein«: all the substances to which I bad an oppor- General coh^ 

 „ ,. . ^ T ^ • • clubions. 



tunity ot extending my expernncnts, 1 must now mquire r 



whether any general conclusions can be deduced from them. 

 And first, as to the value of the different reagents employed 

 as tests. The acetate of lead is by far the most delicate and Acetate ef ' • 

 copious in its effects, but it can be of little value in discrimi- ^^'"^^ ^^^ ^^^^^ 

 nating the different species from each other, because it- prq- notdisciimina- 

 duces its operation almost equally on all of the.a. With t'^^- 

 respect to the super-acetate of lead, we may in the first The superace- 

 place remark how materially it differs from the acetate, with ^^^^greutf ^^^^ 

 which, until lately, it was confounded. The acetate of lead 

 was affected by all the substances to which it was applied, 

 except sugar; while the super-acetate* produced no change 

 upon gum arabic and starch, nor had it any specific effect 

 upon quince mucilage; it was affected only in a slight de- 

 gree by tragacanth, while with the linseed and hyacinth my^ 

 cilage, and with gluten, tolerably copious precipitates weFe 

 thrown down. The nitro-muriate of tin does not act upon xt- 

 gum arabic, but is more or less atiected by every other kind fj/tin. 

 of mucilage, particularly by those of cherry gum, tragi\^ 

 canth, and quince, and by starch of gluten. We have sven 

 in how peculiar a manner the oxysulphate of iron acts.,i|po'n Oxysulphate 

 ^um arabic; it produces a brown colour in a strong solution of 'ron. 

 iif tragacanth ; and it forms a precipitate with th^^ hyacinth 

 and the gluten ; the quince is, as usual, coag\;}ated ; while 

 no change is effected on the linseed or t\^e starch. The 

 nitro-muriate of gold is precipitated by ^ayacinth mucilage ^'gold?""***^ 

 and by gluten; the quince, as in other cases, is cqagulated 

 by it, but its most remarkable effect \s upon the tragacanth, 

 the colour of which it converts to a ^'^ep blackish purple. 



The nitrate of mercnry throw ^ down a precipitate of a sin- ... 

 T ^ X' u- ' . . Nitrate of ai#r- 



gular nature from gum arab .p, and tinges the fluid of a pink cury. 



colour; the same shade is. produced iu the tragacanth, the 



* Dr Thomson raust^ no doubt, have employed this suit, when he 

 :itates, tliat the acetat'^Q^jead does not precipitate gum. 



£> ^ hyacinth 



