348 Dr. Macneven s Exposition oj [Nov. 



no longer dissolve more than 49*8 of carbonate of lime, it follows 

 that lUO crystallized carbonate of potassa are the chemical equi- 

 valent of 50-2 of carbonate of lime, and consequently that 126-5 

 are the equivalent of 63 on the scale. 50-2 : 100 :: 63 : 

 125-5. 



In the next place, if 125-5 crystallized carbonate of potassa 

 be combined with muriatic acid to excess, and that the solution 

 is evaporated until all the water and the redundant acid is 

 driven off, there will remain 93-2 of neutral salt, whether it be 

 called muriate of potassa, or chloride of potassium, or by what- 

 ever name designated, it will always yield 34-1 of dry acid; 

 consequently, the value of the potassa is 59*1. This will contain 

 but 49-1 potassium, which requires 1 of oxygen. 



Another important consideration relates to the composition of 

 the crystallized carbonate of potassa, which Dr. Wollaston, with 

 great propriety, calls bicarbonate of potassa. This name dis- 

 tinctly marks the difference between it and the subcarbonate, 

 and recalls the double dose of carbonic acid which it contains. 

 When compared with the carbonate of lime, it is even neces- 

 sary to consider it as a supercarbonate, for if a solution of this 

 salt be added to a neutral solution of carbonate of lime, there 

 arises a strong effervescence, owing to the carbonic acid exceed- 

 ing the quantity necessary for the saturation of the lime. When 

 125-5 parts of bicarbonate of potassa are saturated with nitric 

 acid, and all due care is taken to prevent any loss of fluid with 

 the gas that escapes, the loss of carbonic acid is 65, or the 

 double of 27-5. But if, before saturation, the salt has been 

 exposed to a low red heat, it sustains a loss of 38-8, viz. 27-5 

 carbonic, and 11-3 of water, after which the addition of an acid 

 drives off but 27-6, or a single proportion of carbonic acid. 



The scale of chemical equivalents is now commonly sold in the 

 book stores of this city, and I cannot too strongly recommend 

 its use. A frequent inspection of it will remind the student of 

 many proportions which he would otherwise forget, and, as an 

 exercise, it will familiarize him with the most important chemical 

 combinations. 



To the practical chemist it gives the composition of any 

 weight whatever of any of the salts contained on the scale, the 

 quantity of any other salt necessary to decompose it, the quan- 

 tity of the new salt that will be formed, and many other similar 

 things that are perpetually occurring. 



The scale itself has various simple and compound substances 

 set down on both sides of ashder that moves through it longitu- 

 dinally. To these substances numbers are annexed, and, by 

 motion of the slider, numerous combinations may be quickly 

 determined, without the intervention of calculation. There are 

 two positions of the slider. 



In the first, 10 on the slider is brought opposite to oxygen on 

 the scale, and other bodies are in their due proportion to oxygen, 



