98 65. BASES AND ACIDS WITH REAGENTS. 



HYDROFERROCYANIC ACID. HCfy. 



65. Ferro cyanides of iron, zinc, manganese, lead, and 

 copper, are insoluble in water ; ferrocyanides of iron and 

 copper are insoluble in dilute acids. 



Reactions* — Ferrocyanides give a deep blue precipitate 

 of Prussian blue, FCgFe^Cy^g, with ferric chloride, which 

 is not soluble in dilute hydrochloric acid, but is decom- 

 posed "by sodic hydrate, the blue color being changed to 

 red. 



HYDROSULPHURIC ACID. HaS. 



66. Sulphurets of arsenic, lead, copper, iron, manga- 

 nese, and zinc, are insoluble in water ; the first three are 

 insoluble in dilute acids. 



Reactions. — Sulphurets give with argentic nitrate a 

 black precipitate, Ag^S, insoluble in dilute nitric acid and 

 in ammonia. 



When sulphurets are treated with hydrochloric or sul- 

 phuric acid, sulphuretted hydrogen, H^S, is evolved Avith 

 effervescence ; the gas may be recognized by its disagree- 

 able odor, and the property of blackening lead-paper. 



HYDRIODIC ACID. HI. 



67. Plumbic iodide is sparingly soluble in cold water, 

 but readily soluble in hot ; other iodides are soluble. 



Reactions. — Iodides give a yellow precipitate, Agl, 

 with argentic nitrate, which is very sparingly soluble in 

 ammonia and in dilute nitric acid. 



If enough potassic dichromate is added to a solution 

 of an iodide to give it a pale yellow color, and then a lit- 

 tle hydrochloric acid, iodine is set free, which, if it is 

 present in notable quantity, gives the solution a darker 



