ilf 



CHEMISTRY. 



tion of 

 Ntnrf. 



milky like mucilage of gum arable when mixed with al- 

 cohol. Acetate of lead throws down a copious dense 

 precipitate. Superacetate of lead and oxymuriate of tin 

 render the liquid opake, and also throw down a precipi- 

 tate. Nitrate of mercury occasions a very slight preci- 

 pitate, while muriate of goW, oxysulphate of iron, and 

 silicated potash produce no sensible eflect whatever. No 

 Change is produced by the infusion of nutgalls. 



(Quince seeds and the root of the hyacinth yield a mu- 

 n with the same properties, with some slight shades of 

 difference, owing probably to the presence of foreign 

 bodies mixed with it. The roots of the hyacinth, vernal 

 -quill, white lily, comfrey, and salop, contain so much 

 mucus, that, when dried, they may be substituted for 

 iim arahic. The leaves of the tualva si/livstrix, many 

 of the fr.ci. and a good many of the stringy lichens, con- 

 tain likewise abundance of mucus. In short, it is one 

 of the most common of the vegetable principles. Pro- 

 bably there are few plants which do not yield some por- 

 tion of it. 



r. VII. Of Jelly. 



JII' Jt we prrss out the juice of black berries, currants, 



and many other fruits, and allow it to remain for some 

 time in a state of rest, it coagulates into a tremulous soft 



How ob- jubstance, well known by the name of jelly. When it is 

 washed with a small quantity of water, and then dried, 

 we obtain it in a state approaching to purity. 



It is nearly colourless, scarcely soluble in cold water, 

 but very soluble in hot water, and, when the solution 

 cools, it again coagulates into a jelly. When long boil- 

 ed, it loses the property of gelatinizing, and becomes 

 analogous to mucilage. When dried, it becomes trans- 

 parent. When distilled, it yields the same products as 

 gum. It seems very intimately connected with gum ; 

 but, as it has never been obtained in a state of complete 

 purity, we are but imperfectly acquainted with its pro- 

 perties. 



SECT. VIII. OfVlmia. 



ll!min. We give this name to a substance lately examined by 



Klaproth. It exuded spontaneously from the trunk of a 

 species of elm, called by him the iilmus ni^ra, and was 

 sent to Klaproth from Palermo in 1802.* 



i-< proper- Externally, it has a good deal of resemblance to gum. 

 It is solid, hard, of a black colour, and has considerable 

 lustre. Its powder is brown. It dissolves readily in the 

 mouth, and has an insipid taste. 



Water dissolves it. The solution has a brown colour. 

 Though very strong, it is not in the least adhesive or 

 ropy, nor does it answer as a paste. It is insoluble in 

 alcohol and ether, and is partially precipitated from water 

 by alcohol. 



When a few drops of nitric acid are added to the aque- 

 ous solution of ulmin, it becomes gelatinous, loses its 

 brown colour, and a light brown substance precipitates. 

 This precipitate is soluble in alcohol, and explodes when 

 moderately heated. Hence, it is a compound of ulmin 

 and nitric acid. Muriatic and sulphuric acids produce 

 . ise yellowish brown precipitates, which are insoluble 

 in water. Ulmin is likewise precipitated by sulphate of 

 iron, muriate of tin, and acetate of lead, but not by ni- 

 trate of silver, nor solution of glue. 



Ulmin when burnt emits little smoke or flame ; it leaves 



a spongy but Arm charcoal, v.'iuli yields, when concco- Chemical 

 trated, a little carbonate of potash. ; ""- 



II,.: 



P. IX. Of Inulin. 



\\ e give this name to a substance discovered by Rose inulin. 

 in the root of the inula bdellium, or clfcamjHinr. Whcu 

 the root of this vegetable was b >iled in water, the decoc- 

 tion, after standing some hours, deposits the inulin in the 

 form of a white powder like starch. 



It is insoluble in cold water. By trituration the inulin In proper- 

 is uniformly diffused, and gives the liquid an opal ap- ''" 

 pearance, but it soon falls down in the state of a while 

 powder, leaving the liquid quite transparent. 



It dissolves readily in hot water. One pan of inulin 

 in four parts of boiling water, formed a solution which 

 passed readily through the filter. After some hours, 

 the greater part of the inulin precipitates from the water 

 in the form of a white powder. 



When the aqueous solution of inulin is mixed with an 

 equal bulk of alcohol, no change takes place for some 

 time ; but the ii.ulin soon separates and falls to the bot- 

 tom in the state of a bulky white powder. A solution 

 of gum arabic, when treated in this manner, remains 

 milky for days without any precipitate falling. 



When thrown upon burning coals, it melts as readily 

 as sugar, and emits a thick white smoke, not unpleasant- 

 ly pungent, and similar in odour to that of burning su- 

 gar. The residue, which is but small, sinks into the 

 coal. Starch emits a similar smoke, but leaves a more 

 bulky residue. When exposed to a red heat, inulin 

 burns with a. vivid flame, and leaves a very small coaly 

 residue. 



When distilled, inulin yields a brown acid liquid, having 

 the smell of pyromucous acid, but not a trace of oil. 



When inulin is treated with nitric acid, it yields malic 

 and oxalic acids, or acetic acid if too much nitric acid be 

 employed. But no saclactic acid is formed as happens 

 with the gums, neither is any of the waxy matter sepa- 

 rated, which makes its appearance when starch is digest- 

 ed in nitric acid. 



SECT. X.- Of Starch. 



If a quantity of wheat flour be formed into a paste, Starcu. 

 and then held under a very small stream of water, kned- 

 ding continually till the water runs off from it colourless, 

 the flour, by this process, is divided into two distinct 

 constituents. A tough substance of a dirty white co- jiowob-, 

 lour, called gluten? remains in the hand ; the water is at Miaul. 

 first milky, but soon deposits a white powder, which is 

 known by the name of starch. 



The starch obtained by this process is not quite free 

 from gluten. Hence it is not very white, and has not 

 that crystallized appearance which distinguishes the 

 starch of commerce. Manufacturers employ a more eco- 

 nomical and more efficacious process. Wheat is steeped . 

 in water till it gives out a milky juice when squeezed, it 

 is then put into coarse linen sacks, which are subjected to 

 pressure in a vessel of water till the whole starchy matter 

 is separated. The sack and its contents are then remov- 

 ed. The water containing the starch gradually ferments. 

 Vinegar and alcohol are formed in it, partly, no doubt, 

 at the expence of the starch. The vinegar thus formed 

 dissolves all the impurities, and leaves nothing behind 

 but the starch. It is poured off, and the starch being 



There 1* no doubt that ulmin exudes from the common elm, nor that it is one of the su'.Mtunre* originally described by Vauqutlu* 

 u ffoctedtng from the ulcer* to whii h (hat true is subject. a 



