APPENDIX. 677 



Because this is the number that gives the atomic weight, and the 

 ratio of the constituents. 



From these examples it will be evident that, in order to have 

 the atomic weight of an acid, we must be able to get it quite an- 

 hydrous. But in many cases we cannot drive off the whole of 

 the water which it contains without substituting some other base. 

 Now oxide of lead and oxide of silver are the two bases that 

 answer best for obtaining anhydrous salts. Oxide of lead is 

 most convenient because it is cheapest. We must determine the 

 weight of water that escapes and the weight of oxide of lead which 

 takes its place. These will bear a certain ratio to each other. 

 If the water be 1-125 and the oxide of lead 14, then the acid is 

 monobasic, and its atomic weight is obtained by simply analyzing 

 its salt of lead, reckoning the weight of oxide of lead in it 14, 

 and calculating the corresponding weight of the acid. If the 

 water displaced be 2-25, and the oxide of lead substituted in its 

 place 28, then the acid is bibasic, and so on. 



What are called ethers are combinations of an atom of acid 

 with an atom of C 4 H 5 O. A good way of determining the atomic 

 weight of an organic acid is to convert it into ether and to ana- 

 lyze in the ordinary way the ether obtained. Being composed 

 of an atom of acid and an atom of C 4 H 5 O, it is easy from that 

 analysis to deduce the atomic weight of the acid. 



The mode of determining the atomic weight of bases is so 

 nearly the same with that of acids that but few remarks are ne- 

 cessary. A given weight of the base dried at 248, may be dis- 

 solved in alcohol. The solution may be mixed with water and 

 the alcohol distilled off. We may then exactly neutralize the 

 base with sulphuric acid, and, by decomposing afterwards by chlo- 

 ride of barium, determine the weight of sulphuric acid capable 

 of saturating a given weight of base. This (if we suppose an 

 atom of base to saturate an atom of acid) gives us data for cal- 

 culating the atomic weight of the base. 



Liebig employs another method, which often answers very well. 

 It consists in causing a current of dry muriatic acid gas to pass 

 through 'a glass tube blown into a ball in which a weighed quan- 

 tity of the base is placed. The increase of weight gives the 

 quantity of muriatic acid which has united to the base, and en- 

 ables us to calculate the atomic weight of that base. The muri- 



