REMARKS ON DR. THOMSON'S CHEMISTRY. 245 



For the rays fall more obliquely upon one of the glades, 

 than upon the other. 



Cor. 3. The direct pencils of rays are but feldom ufed, by 

 a perfon whofe fpe&acles are of the longed focal didance, 

 that will afford hiru didincl virion. ^ 



For he generally looks through thofe parts of his glaiTes, 

 which are remote from their centres, in confequence of that 

 motion which is given to the eyes, to view objects in dif- 

 ferent directions. 



I am, Dear Sir, 



Your mod obedient Servant, 



EZEKIEL WALKER, 



V. 



Remarks on certain Pajfuges in Dr. T/iomfon's Chemijlry, to- 

 gether ivith fome Experiments on Sandarach and Majlic. In 

 a Letter from Mr. R. Matthews. 



To Mr. NICHOLSON. 

 SIR, 



JLN a work of fuch importance as Dr. Thomfon's Chemidry, 



which muft be fo frequently referred to by the lovers of that 



fcience, the flighted inaccuracy ought not to pafs unnoticed : 



the following obfervations therefore, perhaps may be con- InDr. Thomfon's 



iidered fuffieiently interefting to defer ve a place in your cheraift! 7» 



valuable Journal. 



In his 4-th Vol. page 307, Dr. Thorn fon has the. following It is Hated, that 

 remark : '* Hitherto it has been affirmed by all chemids both ^iT afVerted" 

 ancient and modern, that the alkalies do not exert any action thai alcalies do 

 on the refins." This remark I admit may be generally true; ^^ upon 

 but although mod chemids have been negligent in afcertaining 

 the effecls of alcalies upon fubftances of this nature, I con- 

 ceive fome of them were not unacquainted with the power 

 they poflefs of diflblving refinous bodies. 



Boerhaave, for indance, in his elements of chemidry, page The contrary is 

 54-5, exprefsly fays, that, " both the fixed and volatile alcalies jjjj^ b X Bo «" 

 have a diflblving power, upon animal, vegetable, and mineral 

 fubdances, fo far as thefe contain oils, balfams, gums, mjms. 

 ©r gummy rofins, &c," 



3 Hoffmann 



