288 



On Chemical Tests. 



[Oct. 



2 - acid arsemous, the white arsenic of the shops, detects and is 

 detected by hydrosulphurets, and sulphuretted hydrogen gas, with 

 which it produces a yellow precipitate. The liquid contained in the 

 stomach of a rabbit poisoned with three grains of arsenious acid, afford- 

 ed a white precipitate with nitrate of silver, greyish-white with lime 

 water, green with the ammonia-sulphate, and deep yellow with sulphu- 

 retted hydrogen water, see 39. 



a When a particle of arsenic is sublimated between two plates of 

 glass, it forms nebulous patches, considerably like those formed by sul- 

 phur, sublimated in the same manner, but the microscope makes a great 

 distinction between them. The sulphur is globular or semi-globular ; 

 the arsenic is crystallized: this method might be used as an auxiliary 

 in detecting small quantities of arsenic, see 39. 



3. ACID boracic, is indicated by its characteristic green flame 

 when a solution of it in alcohol is set 071 fire. To distinguish a borate 

 from other salts, digest it in sulphuric acid slightly in excess, evaporate 

 to dryness, and digest the residue in alcohol, which dissolves the boracic 

 acid set free by the sulphuric acid, and its presence is then indicated 

 as above. Boracic acid turns turmeric paper brown ; it has but a slight 

 action on litmus paper. 



4. AGED carbonic, is detected by barytes, see 40 e. By lit- 

 mus, see 77. By lime water, see 75 ; By sulphate of iron, see 67 b. 

 and by the mineral acids which drive it off, or set it free with efferves- 

 cence, see lie, 13 g, and 18 g. Carbonic acid detects lime in so- 

 lution, precipitating it as carbonate of lime. Carbonates may be easily 

 distinguished from other salts, by their effervescing without smell, on 

 the addition of a mineral acid ; see 45 iglf. 



5. ACID chloric, or hydro- chloric, see 11. 



6. ACID chromic, see 48. 



7. acid fluoric, see 18 a, and 54. 



8. ACID gallic, detects iron in solution, forming ink. The solution 

 should be of the per-oxide of iron for the test to act immediately, see 

 55. Gallic acid may be distinguished from tannin by producing no pre- 

 cipitate when added to a solution of gelatine. 



