482 SCIENCE PROGRESS. 



filtered on a hot filter. The residue is then macerated for 

 twenty-four hours in 2 per cent, hydrochloric acid, and 

 pressed dry. The acid liquid dissolves the pectine. After 

 filtration an equal volume of strong alcohol is added and 

 the pectine is thereby thrown down as a flocculent precipitate. 

 This is gathered on to a filter and washed with alcohol to 

 which 2 per cent of hydrochloric acid has been added. To 

 free it from the acid it is then dissolved in water and pre- 

 cipitated by alcohol, the process being repeated several 

 times. As the acid disappears the pectine becomes more 

 and more gelatinous, and will ultimately pass over into a 

 colloidal state. This is prevented by not carrying the 

 washing too far, but neutralising the last trace of acid 

 with a weak alkali. 



The action of the enzyme, or pectase, described by 

 Fremy as producing pectosic and ultimately pectic acid, 

 seems in the light of the work of the last quoted observers 

 to be dependent on the presence of a small quantity of a 

 soluble calcium salt, the resulting body not being pectic 

 acid, but its calcium compound. The clot or jelly produced 

 is insoluble in weak alkalis, but dissolves readily after being 

 macerated in weak hydrochloric acid, and the solution is 

 found to contain a small quantity of lime. 



The application of the lime or other earthy alkaline salt 

 in the coagulation needs careful watching, for if too great a 

 quantity be added other gelatinous pectinates are produced. 

 They can be distinguished from the proper coagulation 

 product by being treated with weak hydrochloric acid, 

 which displaces the pectic acid and the pectinate. If 

 only the latter form the jelly, everything goes into solu- 

 tion ; but if the pectate of calcium has been formed, pectic 

 acid is set free by the acid, and this is insoluble. 



Pectic acid, indicated by Fremy as the ultimate product 

 formed during the coagulation or gelatin isation, is the oldest 

 known of these bodies and gives the most distinctive re- 

 actions. It is insoluble in water, in alcohol, or in acids ; it 

 forms compounds (pectates) with the alkalis which are 

 soluble in water, and others with the alkaline earths which 

 are insoluble. The lime salt is the most widespread in 



