ION THE PURITY OF THE FIXED ALKALIS. 3| 



This last observation explains how it comes to pass, that 

 a. tree, when its age is doubled, the i*ate per cent per annum 

 that its increase then bears to the contents of the whole tree, 

 IS diminished one half. 



It may not be unuseful to observe, that the rate per cent 

 of increase in the last columns, is the same as the rate per 

 cent that the increase of the tree that year will pay for the 

 money it was worth the preceding- year. 



[ii the two preceding tables, we find that the rate of in- 

 crease per cent per annum is the same in both at the same 

 ages, although the quantity of timber in the second table 

 is six times as much as in the first table in trees of all ages; 

 therefore, when the age of a tree is known, the rate per 

 cent per annum of its increase is known on inspecting these 

 tables, whether the tree has grown fast or slow; provided 

 the growth of the tree has been regular, and that it has 

 continued ity usual growth. 



And having the age, girth, and height of any tree given, 

 we can readily calculate what quantity of timber it will 

 contain at any future period, while it continues its usual 

 rate of growth. 



fTo be continued. J 



IV. 



Observations on Potash and Soda prepared with Alcohol : by 

 Mr. d'AacET. Read to the Institute the II th of January., 



1808.* 



HEN chemistry, employing new rrethods of analysis, 

 is enriching itself with important facts; when England an- 

 nounces the decomposition of potash and soda, and the 

 chemists of France are busied in confirming this grand dis- 

 covery; I conceive it incumbent on me to communicate the 

 results of vai-ious experiments, which may probably throw 

 some light on the path newly opened. 



* Annales de Chimie, vol. LXVIII, p. 175, 



I present 



