38 Description of an improved Air-Pump. 
and which has much resemblance to that of burnt onions, 
M. Antoine, however, compares it to the odour of caramel, 
The alkalis form with it soluble salts, and that of soda, 
among others, of a fresh savour, slightly bitter, and which 
leaves in the mouth a taste like that of green nuts. 
Barytes, strontian, or lime, united to this acid give very 
insoluble salts, susceptible of solution in an exceys of acid, 
but difficultly: all of them present themselves under the 
form of flakes more or less light. It possesses the remark- 
able property of decomposing, in general, all the earthy 
acetates without having recourse to Wolibite affinities; it also 
decomposes several metallic solutions, and in a remarkable 
manner those of iron, which it precipitates white though 
at the maximum ; those of copper it precipitates of a blueish 
green. The acetate of lead is also precipitated in white 
flakes, which are tasoluble in vinegar. 
If in place of employing this free acid we take one of iis 
alkaline combinations, precipitates are obtained, in the so- 
lutions, of aluminous and magnesian salts; but it is neces- 
sary that the latter be very much concentrated, without 
which ae precipitates are redissolved immediately. 
[To be continued. ] 
VIII. Description of an improved Air-Pump. By 
T. SytvesTER, Esq. 
To Mr. Tilloeh, 
SIR, 
Oe of the principal causes of the imperfections in the 
air-pump arises from the difficulty i in opening the valves at 
the bottom of the barrels, which imperfection was thought 
to have been remedied by the introduction of stop-cocks ; 
but experience shows that, however accurate they may ud 
when new, after a little use they became faulty. 
{ here send you a description of an air-pump, which I 
lately executed, without either valves or stop-cock. I have 
supplied their place by a slide, which is shifted at every mo- 
tion of the piston, in a similar manner to that of a stop~ 
cock, which requires no pressure of the air to open it. It 
moves between two facings of Icather, which lessens fric- 
tion 
