350 Scientific Proceedings^ Royal Dublin Society. 



tannic acid to precipitate albumins. The juice was filtered, and centrifuged 

 until almost clear. The pectin was precipitated by addition of an equal 

 volume of alcohol, and was filtered ofE and redissolved by pouring a little 

 hot water on to the filter. The pectin was subsequently repreoipitated by addi- 

 tion of alcohol, and the gelatinous precipitate obtained was collected by means 

 of a centrifuge and dried on a watch-glass placed on a water-bath. A horny 

 residue was obtained in this way, and about 0-3 g. of pectin was extracted 

 from about 1100 g. of carrots. 



In subsequent extractions the carrot-roots were finely minced, and the 

 pulp covered with water, and heated on a water-bath for one or two hours. 

 The pulp was then squeezed, and tlie liquid obtained was treated as before. 

 This method was based on one described by Bourquelot and H^rissey (5), 

 who obtained pectin by heating chopped-up gentian roots with water in an 

 autoclave at 110° C. 



Browne (7) recommends the addition of tannic acid to juice which has 

 been extracted in the cold. In cases where the carrot pulp had been heated 

 this was found to be unnecessary, as all albuminous substances had been 



Tlie pectin obtained from these various extractions was dissolved in 

 sufficient water to form a 2 per cent, solution, and a few drops of toluene 

 were added to prevent growth of micro-organisms. The pectin solution thus 

 obtained was in a fairly pure state, but was faintly acid to litmus paper. In 

 all the experiments this solution was diluted with an equal quantity of 

 water. 



Sap pressed from the leaves of Syringa vulgaris was used exclusively as a 

 source of pectase. Tliis plant was chosen both for the sake of convenience, as 

 the leaves could be obtained easily, and also owing to the fact that Bertrand 

 and Mall^vre (4) state that sap pressed from these leaves is fairly active in 

 coagulating pectin. 



The method of extraction was as follows : — Leaves were stripped from 

 fresh shoots of Syringa, the petiole of each leaf being removed. They were 

 then placed in a small steel cylinder fitted witli a piston, and provided with 

 a hole at its lower end. The piston was squeezed in by means of a vice, 

 and the expressed sap was centrifuged until clear, and was then ready 

 for use. 



Measurement of the electrical conductivity during tlie coagulation of pectin. — 

 If the product of the action of pectase on pectin is a true gel, there would 

 be little change in electrical conductivity during its formation, as the 

 resistance of a gel to the passage of ions is practically the same as that of the 

 sol from which it has been formed. 



