HYDRATES AND CARBONATES OF THE ALKALI- METALS, ETC. 



441 



2. 



3. 



4-994 



- 52 per cent 



4989 



0-62 



4-953 



1-34 



4-984 



0-72 



4-994 



0-52 



4-987 



0-66 g „ 



4-951 



1-38 "" „ 



4-985 



0-70 



4-993 



0-54 



known as "Planner's Spinne." The general modus operandi was, to take a known weight 

 of the respective carbonate (previously dehydrated at a dull red heat) and expose it 

 successively to the stated standard temperatures, taking care at each step to continue 

 the heating until the weight of the residue was constant. The platinum crucible was 

 provided with a close-fitting concave lid, to avoid loss by creeping and volatilisation 

 as far as thus possible. His experiments with carbonate of soda may be quoted in detail. 

 Weight of dehydrated carbonate operated upon, 5 '020 grm. These, when exposed 

 successively to the temperatures named, in column 1 of the following Table, assumed the 

 constant weights given in column 2 ; column 3 gives the losses of weight suffered by 

 the carbonate, in percentages of its original weight. 



1. 



1. Eothgluth, 



2. Orangegluth, 



3. Gelbgluth, 



4. Orangegluth, 



5. Eothgluth, 



6. Orangegluth, 



7. Gelbgluth, 



8. Orangegluth, 



9. Eothgluth, 



The most remarkable feature in these results is that each of the three temperatures 

 corresponds to very nearly a constant weight characteristic of the respective temperature ; 

 the additional loss of weight, which took place in passing from 1. to 3., was undone by 

 re-establishing the " Rothgluth" of stage 1. According to Scheerer "there can be no doubt 

 that the matter which left the carbonate of soda in the heat, and (the matter) which 

 was taken up again when it passed from higher to lower temperatures, was carbonic acid. 

 It cannot reasonably be presumed to have been water.* We must admit that the ratio 

 of the equivalents of soda and of carbonic acid is a function of temperature. Taking the 

 equivalent of the former as constant and = Na 2 0, that of the latter, at "Gelbgluth," is 266, 

 instead of 275 as at the ordinary temperature (0= 100). In solid carbonate of soda, as it 

 is at ordinary temperatures, 1000 atoms of soda are combined with 1000 atoms of C0 2 ; 

 at "Gelbgluth" 1000 atoms of soda unite with 967 atoms of carbonic acid." 



With carbonate of potash he obtained similar results. The salt, previously dehydrated 

 at a dull red heat, lost 0*25 per cent, of its weight at " Orangegluth" and further 0*50 

 per cent, on subsequent exposure to "Gelbgluth" and these 0'5 per cent, were taken up 

 again when " Orangegluth " was re-established. 



This is the substance of Scheerer's results as far as they are in contact with the 

 present investigation. 



In my own experiments the general order of operations was as follows : — In a first 

 series of experiments the respective carbonate was exposed for a shorter or longer time to 

 a red heat in an atmosphere of pure hydrogen, which in all cases led to the production of 



* ? Vide infra. 



