16 § 13- HE A GENTS. 



evaporate the solution to expel excess of acid, and dis- 

 solve the residue in 10 parts of water. 



d. Ferrous chloride. — FeCl„. (Protocliloride of iron. 

 FeCl.) — Dissolve pianoforte wire in concentrated hydro- 

 chloric acid ; the solution should be made as it is wanted. 



e. Ferrous sulphide.— FeS. (Sulphide of iron.)— Get 

 the fused sulphide of the druggists. 



13* Hydrogen. — II. — This is made by the action of di- 

 lute sulphuric acid on granulated zinc. To purify the gas 

 conduct it through a U tube, or a calcic-chloride cylinder, 

 containing freshly ignited charcoal, and in order to dry 

 it, through another cylinder containing calcic chloride. 



14. Indigo solution. — This may be prepared by treat- 

 ing 1 part of finely powdered indigo with 5 i)arts of 

 fuming sulphuric acid 48 hours in the cold, and pouring 

 the mixture into 20 parts of cold water. 



15. Iodine. — I. — This needs no testing. 



16. a. — Iron Turnings. — These should be clean and 

 free from grease. 



h. Iron wire. — Get the finest pianoforte wire, free from 

 rust. 



17. a. — Lead-paper. — Soak slips of unsized paper in a 

 solution of i^lumbic acetate, dry, and keejD in a well stop- 

 pered bottle. 



h. Litmus-paper (blue). — Digest litmus Avith G parts of 

 water, filter, divide half of the filtrate into two equal 

 parts and carefully saturate the free alkali in one of these 

 parts with sulphuric acid, until the liquid has taken a red 

 color that docs not disappear after standing a few min- 

 utes ; add the other part to this, color strips of unsized 

 paper in the blue liquid, dry them, and keep in a dark 

 place. The strips should have a blue color. 



c. Litmus-paper (red). — Add sulphuric acid to the 

 other half of the extract of the litmus until a i^ermanent 



