Dr Davy's Miscellaneous Chemical Observations. 131 



7. On the Taste and Smell ofBoracic Acid. 



Dr Thomson states, (on the authority of other chemists), that 

 boracic acid has " a sourish taste at first, then makes a bitterish 

 cooling impression, and at last leaves an agreeable sweetness *." 

 The taste of this acid to me is bitterish, not unlike that of Ep- 

 som salts ; and I have perceived no after sweet taste. 



The same author states, that boracic acid *' has no smell ; but 

 when sulphuric acid is poured on it, a transient odour of musk 

 is produced."" On repeating this experiment, I have never been 

 able to detect this odour. 



He states farther, that " it reddens vegetable blues." When 

 I have tried it, it has reddened them very slightly ; and has ren- 

 dered turmeric brown like an alkali, which, if I recollect right- 

 ly, has been noticed by Mr Faraday ; but I am not sure of it. 

 [Mr Faraday has noticed that it renders turmeric paper brown 

 like alkalies. — Edit.] 



8. On Borat of Silver. 



Dr Thomson says, " borat of silver may be formed, by pour- 

 ing a solution of borax into liquid nitrate of silver. The salt 

 falls to the bottom in the form of an insoluble white powder, 

 which has not been examined." 



I find that boracic acid does not precipitate silver from the 

 nitrate ; and also, that, if the excess of base in borax is neutra- 

 lised by boracic acid, or nitric acid, it does not precipitate nitrate 

 of silver. It may be inferred, therefore, that the precipitate al- 

 luded to by Dr Thomson is either oxide of silver or af triple 

 salt. 



9. On the Purgative Quality of Glauber Salt, as connected 

 with the Sulphat of Iron it contains. 

 Out of six different specimens of Glauber salt which I have 

 examined, I have found five to contain a small quantity of iron, 

 (probably the sulphat), and one only free from iron. The iron 

 was detected by aqua ammonia added to the salt in solution ; it 

 occasioned a yellowish brown precipitate. Dr Paris, if I recollect 

 righdy, in his Pharmacologia, expresses it as his opinion, that 



• Opus cit. iL 91. 



I 2 



