450 CASTOR OIL 



off as it rises to the surface a process which yields, how- 

 ever, an inferio and dark-coloured specimen. The Conti- 

 nental plan of extracting the oil by alcohol or carbon 

 bisulphide is expensive and inconvenient. 



PROPERTIES. Oil obtained by these various methods 

 differs slightly in activity, but considerably in colour, flavour, 

 solubility, and keeping properties. Cold-drawn castor oils, 

 prepared by expression alone, or with only a very slight 

 degree of heat, are generally preferred. 



Castor oil, when fresh and well prepared, is viscid, almost 

 colourless, and of a faint oily odour and taste. Although 

 lighter than water, it is one of the heaviest of the fixed oils, 

 its specific gravity being O950 to 0-970. Exposed in a thin 

 layer it thickens, gets rancid, and after a time entirely dries 

 into a varnish-like film. Castor oil and alcohol are mutual 

 solvents ; the oil is soluble in one volume of absolute alcohol 

 and five of alcohol (90 per cent.), and in ether ; is easily 

 miscible with other oils ; saponifies with alkalies, yielding 

 glycerin, palmitic, and other fatty acids, and the special 

 ricinoleic acid. Thus saponification, caused by the alkaline 

 secretions of the bowels develops, as in the case of croton oil, 

 the irritant, active principle from the bland oil. 



IMPURITIES. Castor oil is adulterated with croton oil to 

 increase its activity, with lard and bland oils to reduce its 

 cost. Inferior sorts are dark-coloured, but become trans- 

 lucent by exposure to sunlight and filtration through animal 

 charcoal ; while the disagreeable acrid taste and odour may 

 in great part be removed by repeated agitation with water 

 containing calcined magnesia and coarse animal charcoal. 



ACTIONS AND USES. Castor oil seeds are irritant and pur- 

 gative, and have caused fatal gastro-enteritis both in human 

 patients and in animals. This irritant action is due to the 

 presence of the t ox-albumin ricin. This substance is 

 extremely toxic if injected intravenously, less so given 

 subcutaneously, and is largely neutralised by the gastric 

 juice, and rendered harmless when given by the mouth. 

 It may, however, escape this neutralisation, and will then 

 exert all its toxic effects. It causes vomiting and diarrhoea, 

 and post mortem the mucous membrane of the intestine is 

 found inflamed, and there are haemorrhages into the serous 



