OILS 433 



removed, and the oil again collects. By the prolonged action of ammonia, however, 

 on the oils, true ammoniacal soaps are formed, and at the same time a peculiar body 

 is formed, called by its discoverer (Boullay) margaramid. 



It is obtained by boiling the ammoniacal soap with water, when the margaramid 

 swims on the top, and when allowed to cool solidifies. It is purified by solution 

 in boiling alcohol, which deposits it again on cooling in the crystalline state. It is a 

 white, perfectly neutral solid, unalterable in the air, insoluble in water, very soluble 

 in alcohol and ether, especially by the aid oflieat. It fuses at about 140 Fahr., and 

 burns with a smoky flame. It is decomposed when boiled with potash or soda, forming 

 true soaps, with the liberation of ammonia, and also by acids of a certain degree of 

 concentration. 



The alkaline earths and some metallic oxides unite with the fatty acids, forming 

 insoluble soaps, which in the case of lead is called a plaister. 



After glycerine and the fatty acids have once been separated, they do not readily 

 again unite ; but Berthelot has succeeded in effecting this, by enclosing them for a 

 considerable time in a sealed tube, and subjecting them to a more or less elevated 

 temperature, when the true oils are again produced. 



Action of Acids upon the Oils. Sulphuric acid (concentrated), when added to the oils, 

 unites with them energetically ; the mixture becomes heated, and, unless cooled, chars 

 with the liberation of sulphurous acid. When the mixture is cooled the fats and oils 

 undergo a similar change to that which the alkalis effect. There is formed some 

 sulpho-glyceric acid, as well as combinations of margaric and oleic acids with sul- 

 phuric acid ; these latter are again decomposed when mixed with water, liberating the 

 fatty acids. 



Nitric Acid (concentrated) attacks the fatty bodies very rapidly, sometimes causing 

 ignition. Dilute nitric acid acts less powerfully, forming the same compounds which 

 we obtain by acting on the several constituents of the oils separately. 



Hyponitric acid, or nitrons acid, converts the oleine of the non-drying oils into a solid 

 fat, elaidine. 



Chlorine and bromine act on the fatty oils, producing hydrochloric and hydrobromic 

 acids, and some substitution-compounds containing chlorine or bromine. 



When moist chlorine gas is passed into the oils, the temperature rises, but it does 

 not cause explosion. Bromine, on the contrary, acts with violence. The chlorine and 

 bromine products thus obtained are generally of a yellow colour, without taste or 

 smell. They are heavier than water, and possess a greater consistence than the pure 

 oils. Exposed to the air when slightly heated, they become considerably harder. 



Iodine also attacks the oils forming substitution-compounds. 



The fatty oils are divided into two classes, drying and non-drying oils, which are 

 characterised by their different deportments when exposed to the atmosphere. In close 

 vessels, oils may be preserved unaltered for a very long time, but with contact of the 

 atmosphere they undergo progressive changes. Certain oils thicken and eventually 

 dry into a transparent, yellowish, flexible substance, which forms a skin upon the 

 surface of the oil and retards its further alteration. Such oils are said to be drying, 

 or siccative, and are on this account used in the preparation of varnishes and painters' 

 colours. Other oils do not dry up, though they become thick, less combustible, and 

 assume an offensive smell. These are the non-drying oils. In this state they are called 

 rancid, and exhibit an acid reaction, and irritate the fauces when swallowed, in conse- 

 quence of the presence of a peculiar acid, which may be removed in a great measure 

 by boiling the oil along with water and a little common magnesia for a quarter of an 

 hour, or till it has lost the property of reddening litmus. While oils undergo the 

 above changes, they absorb a quantity of oxygen equal to several times their volume. 

 Saussure found that a layer of nut-oil, one quarter of an inch thick, enclosed along 

 with oxygen gas over the surface of quicksilver in the shade, absorbed only three times 

 its bulk of that gas in the course of eight months ; but when exposed to the sun in 

 August, it absorbed 60 volumes additional in the course of ten days. This absorption 

 of oxygen diminished progressively, and stopped altogether at the end of three months, 

 when it had amounted to 145 times the bulk of the oil. No water was generated, but 

 21 '9 volumes of carbonic acid were disengaged, while the oil was transformed in an 

 anomalous manner into a gelatinous mass, which did not stain paper. To a like ab- 

 sorption we may ascribe the elevation of temperature which happens when wool or hemp 

 besmeared with olive or rapeseed oil, is left in a heap : circumstances under which it 

 has frequently taken fire, and caused the destruction of cloth-mills and other buildings 

 and ships. 



Although most of the fixed oils and fats are mixtures of two or more of the sub- 

 stances, oleine, margarine, and stearine, yet there appear to be different modifications of 

 these substances in drying and non-drying oils; for instance, it is only the oleine of the 

 non-drying oils that solidifies when treated with nitrous acid or nitrate of mercury; 



VOL. III. F F 





