§ 18. HE AGENTS. 17 



red color is just obtained ; color 'slips of unsized paper in 

 this solution, dry them, and keep in a dark place. The 

 strips should have a distinct red color. 



18. a. — Magnesia (calcined). — MgO. — This should be 

 freshly ignited before being used. 



h. Magnesia mixture. — ^Mix together 1 part of raag- 

 nesic sulphate, MgSO^, 1 of amnionic chloride, 4 of am- 

 raonic hydrate, and 8 of water; let the mixture stand 

 several days in a moderately warm j)lace, and decant the 

 clear solution for use. 



19. Malt. — Get good brewer's malt. 



20. Manganic binoxide. — MnO„. — The commercial, na- 

 tive, crystallized binoxide of manganese is generally suf- 

 ficiently pure. 



21-. «.— Mercuric nitrate.— Hg (NO 3) „. (Nitrate of 

 mercury. HgO,KO^.) — Dissolve mercury in its own 

 weight of nitric acid (Sp. Gr.=1.4), heat the mixture to- 

 wards the close of the operation, and, finally, add to it 

 twice its bulk of water. 



K Mercurous nitrate.— Hg^(N"03)2.—(Subnitrate of 

 mercury. Hg^O, NO^.) — Pour 1 part of pure nitric acid 

 (Sp. Gr.=1.2) over 1 part of mercury, let stand 24 hours 

 in a cool place, separate the crystals from the undissolved 

 mercury and the mother-liquor, dissolve them in water 

 mixed with ^1^^ of nitric acid, by trituration in a mortar, 

 filter, and keep the solution in a bottle with metallic mer- 

 cury covering the bottom. 



MicroCOSmic salt. — ^cg sodic ammonic phospJiate. 



Milk of lime. — See calcic hydrate. 



22, Oxygen. — O. — Mix together in a mortar 100 grms. 

 of potassic chlorate and 0.1 grm. of ferric oxide, half fill 

 a retort with the mixture, and heat over a coal fire, at first 

 gently. As soon as the contents of the retort are partly 

 fused, mix them together by gentle iagitation. Collect 



