ON FACILITATING THE GROWTH OF ROOTS FROM LAYERS. 3 13 



is, mistakenly, attributed to the coolness of the lead ; but the 

 true cause is as above mentioned. The evil would, in all pro- 

 bability, be much more considerable, were it not for the pre- 

 sence of the saccholactic acid, which takes the lead from the 

 acetic acid, and forms an insoluble compound, 



IK Copper. 



The only other metallic substance likely to be taken into the Copper, 

 stomach is copper ; and for this the beautiful blue colour pro- 

 duced in its solutions by pure ammonia, is the most decisive Ammonia its 

 and satisfactory evidence that can be required, proper 



As a general reagent, either for the present metal, or for ggj^^^.^, ^^^j^f 

 lead, mercury, or arsenic, none, in point of delicacy, can metallic poi- 

 CKceed liquid sulphuretted hidrogen. It detects the smallest ^°"*' 

 quantity of m.etallic matter present in any mixture ; and 

 although the coloured media, in which experiments of this 

 sort are generally obliged to be made, prevent thai reliance 

 upon the mere colour of a precipitate requisite to give this test 

 an exclusive preference ; yet it may frequently abridge the 

 labour of an operation very considerably, and at once decide whe- 

 ther the poison has been metallic or otherwise. In conducting Q^neral pre- 

 this sort of experiments, the recommendation of Dr Bostock, cautions. 

 to view the result by rejiecled, and not by transmitted, light, 

 is highly important j and in no case, perhaps, ought a decision 

 to be given without comparing the effect of every test on the 

 suspected mixture with the phenomena it presents in fluids of 

 known composition. 



XII. 



On facilitating the Emission of Roots from Layers. By T. A. 

 Knight, Esq. Pres. H. S*. 



T is my custom, annually, to repeat every experiment that Experiments 

 occurs to me, from which I have reason to expect in forma- °" '^^„f "•f** 



, . _ , iion diici ino- 



tion either in opposition, or in favour, of the opinions I have don of sap ia 

 advanced respecting the generation and motion of the sap in trees. 



* Trans, of the Hort. Soc. toI. I. p. 255. 



trees ; 



