LECT. III.] THE SAP. 109 



ratio of the distance, which appears in some degree 

 to arise from the solution of deposited matter in 

 its progress, but, perhaps, more from the transpi- 

 ration of the plant throwing off a large proportion 

 of the watery part of the matter taken up from 

 the soil. Such are the sensible qualities of sap ; 

 its chemical properties and composition are dis- 

 covered by tests and analysis by heat. I shall first 

 mention some experiments I made on the sap of 

 the Vine, and then detail the results of those made 

 on some other saps by Vauquelin a celebrated 

 chemist of the French school. 



On the eighth of April, when the thermometer 

 was at 68, and a few leaves of the Vine, which 

 was the subject of experiment, had already ex- 

 panded, I cut off the extremity of the lowest 

 of the branches, and introduced the cut end of 

 the part which remained fixed to the Vine, into a 

 six ounce Apothecaries' phial. On the following 

 morning, about three ounces of a clear, limpid, 

 colourless fluid, like water, was found in it. It 

 had no perceptible taste, except a slight mucila- 

 ginous feeling on the tongue ; no odour ; and 

 weighed rather heavier than distilled water. On 

 pouring a little of the Tincture of Litmus into it, 

 it was very slightly reddened, thereby indicating 

 the presence of an acid *. The oxalic acid almost , 



* Dr. Prout, who examined the sap of the Vine, found that 

 the specimen which he procured did not differ in specific gravity 

 from pure water ; nor did it alter Litmus paper. 



