418 



- !' IS, V. 



l AIXK OILS. 



of the mcni interact, M being the salt from which the 



.,- ; . - :..!.. 



* : u it found in lemons, in great banoMioe, 

 of which it m.iy be obtain.' I l.y a I lin,' 

 rhalk, which affords a citrate of lime. Dilute sulphuric 

 acid u to be ! 



decomposed. The citric aciil in iy be crystallised from 

 the remaining li.pi.l. In the anhydrous state, the for- 

 mula for ci-nc ad.l is C, 3 H, O,., but it U in a en 

 Iwod state unit-d with five equivalents : I 1 "'"- 



doced above. Its proper constitution, however, may bo 

 -aented by the addition of three equivalents (3HO) 

 .a above formula. Citric acid unites with bases, 

 itrates, of which the alkalies are soluble, whilst 

 thoM of the earth* are insoluble in water. 



ACID. The ordinary oak-bark, call-nuts, cate- 

 , contain two acids, the gallic and tannio, 



which have considerable co lereial importance, inas- 



i as the tauuing of leather, the manufacture of 

 ink, ami photographic processes, depend on them. 



U ilhc acid may be procured by allowing an infusion of 

 powdered nut-galls to be exposed to the air, until the 

 whole .volution. Arc,, has become completely mouldy : from 

 this, gallic acid may be dissolved out and crystallised. 

 now prepared in large quantities as a photograplu'o 

 agiiit, being much used in developing pictures by various 

 ]..,.. - , .. 



When gallic acid is heated, another acid, the pyro- 

 gallic, U produced, which is also largely used in photo- 



graphy. The formula for gallic acid is C, HO 8 + 2HO ; 

 that of t!..' ' ' " . 



TAKVIO A. -n> C, 8 H, O 9 + 3 HO is the active agent 

 -hark, nut-galls, sumac, A;c., which renders them so 

 v.i u. il' e in the in i!iuf:ieture of leather :ind iuk. It has 

 the property of precipitating gelatine, ,tc., us found in 

 skins, as an insoluble substance. In the process of tan- 

 ning, the gelatine of the skins is thus transformed, and 

 y rend-red not liable to further change. 

 \\ 'ith the oxide of iron a black colour is produced ; and 

 hence the usual method of making ink, and of dyeing 

 textile fabrics of a black colour, is that of employing so- 

 lutions of iron, and infusions of substances containing 

 tanuic acid. The acid is generally obtained by means of 

 the action of ether on nut-galls. The liquid is add 

 the powdered nut, and the solution of acid is allow . 

 evaporate spontaneously, when it will afford crystal? of 

 the acid. 



With the exception of the tannates of iron, as in ink, 

 ami dye products, the tanuatos and gallatus are of no 

 importance. 



\Vo have thus presented descriptions of the chief 

 vegetable acids to which the attention of the student 

 mied be directed. Some of them, as we have seen, are 

 of considerable commercial importance. Their salts are 

 all decomposible by the mineral acids, by means of 

 which the organic acids themselves may generally be set 

 free, and obtained in an isolated form. lu almost every 

 case they may be had in crystals. 



CHAPTER X. 

 MISCELLANEOUS VEGETABLE SUBSTANCES. 



OILS, RES1XS, COAL AND ITS PRODUCTS, PARAFFINS, BOCK-OIL, PETROLEUM, VEGETABLE COLOURING MATTER, 



ANILINE, ETC. 



WF. shall now briefly describe a variety of vegetable pro- 

 i.lerable use for numerous purposes, and 

 1 from various sources, either during the growth 

 or from the decay of plants. 



OILS Vegetable oils much resemble those obtained 



.iinals in many respects. They give a greasy stain ; 



if of the "fixed" kind, are inflammable, of light specific 



gravity, and consist chiefly of carbon and hydrogen; hence 



.10 for illuminating purposes. 



The fifed oils such as that of the olive or almond, itc. 

 are distinguished from the volatile by many qualities. 

 They cannot IH> distilled except at a high temperature, 

 1 and then they are generally decomposed. The volatile, 

 such as oil of lavender, or otto of roses, readily evapo- 

 rate, even at ordinary temperatures. If a drop of otto of 

 rune* and one of olive oil be placed on blotting-paper, the 

 essential oil will speedily evaporate by a gentle heat, 

 whilst the fixed oil stains the paper with an unctuous 

 mark. It U customary to adulterate the otto with sper- 

 ma< the above plan affords a ready means .of 



detecting the imposition ; for, if any of the spermaceti 

 be present in a specimen of the otto, the volatile oil will 

 pass olf, whilst the fatty matter remains on the paper. 

 Generally speaking, the oils derive their names from 

 lant producing them ; and the following gives a de- 

 scription of the bent known substances of each class. 



FIXED OILS. These oils consist chiefly of two distinct 

 substance* : one a fluid, to which the name olriiir is ap- 

 plied ; and the other a solid matter, termed tttarinc and 

 marynrine, when obtained from animal substances, or 

 palmitine or cOcine, when produced from vegetable, as 

 the palm or cocoa-nut. Vegetable oils are generally 

 obtained from the fruit or seeds of the plant. Thus, 

 e oil is expressed from the fruit ; whilst rape, linseed, 

 ' cantor, Ac., afford oil from the seed. Their chemical 

 i composition varies considerably. Generally speaking, 



I they contain about equal proportions of carbon and 

 hydrogen, a little oxygen, and an equivalent of water. 



i Some are nearly solid, as palm oil, at ordinary tempera- 

 tures ; but even the most fluid become semi-solid on ex- 

 posure to a temperature of 32, as is familiarly known in 

 the case of salad oil, the most fluid, which " frce/.es" in 

 winter-time. Some oils, by the absorption of oxygen, 

 become what are termed "drying oils," such as linseed, 

 which, if boiled with litharge, affords the drying oil 

 used by house-painters. All lixud oils are insoluble in 

 water ; most form soap with that fluid, or i <, by 



the agencies of alkalies ; and some are soluble in alcohol 

 and ether. 



Vegetable wax is obtained from some plants belon 

 to the family Myruacea, itc., and largo qnani ii ies of this 

 substance are now imported from Japan, South America, 

 and the Cape. 



The following table gives the specific gravity of some 

 vegetable oils, water =1,000 : 



Rape oil 913 



Colza 914 



Olive 916 



Almond (sweet) 917 



Poppy fl--' 



Sunflower 926 



Cocoa !>-'(> 



Linseed 9JO to "ini 



Castor . %."> 



Although the specific gravity of the fixed oils is the 

 method of distinguishing them, the action of sulphuric 

 acid in a concentrated state has been proposed. One 

 drop of the acid u added to a few of the oil to be 

 cx.-miined, and the reaction may be carefully noticed. 

 Each oil presents a distinct effect, at once characteristic 

 of its nature. The subject, however, is one into which 

 we cannot here enter in detail.* 



Olive M is the produce of the Oka Enroptea, and is 

 obtained from the fruit by pressure and fermentation. 

 BM Article, Artificial III" s-ct. II. 



