CHEMICAL MICROSCOPY 



aqueous solutions, when a high concentra- 

 tion of iodine is wanted, 



(a) I-KI, 10:10 (g in 100 ml). This is 

 saturated with iodine; often the most useful 

 ratio for crystals, although iodine evaporates 

 from it comparatively readily. Also the more 

 dilute solution (1:1) is chiefly used for 

 complex compounds (such as alkaloids). 



(b) I-KI, 5 : 14. Used for atropine in trace ; 

 also, added to bicarbonate solution and with 

 added KCl (or other similar cation), for 

 caffeine, theobromine, etc. 



(c) I-KI, 10:50. Used for colchicine (neu- 

 tral or bicarbonate solution) ; etc. 



(7) A series of aqueous ^'alkaloidal" iodine 

 reagents. The precise ratio of iodine to iodide 

 has usually been ignored as an important 

 factor, and is sometimes not even stated. 

 However, it is vital. Using 1 g iodine to 

 make 100 ml solution, the following amounts 

 of KI give distinctly different reagents, of 

 declining sensitivity (of precipitation) in 

 some cases, and different crystals in many 

 cases: 1 g; 1.75 g; 2.75 g; 5 g; 10 g; 20 g; 

 35 g; 50 g. Dissolve the iodine and KI in no 

 more water than necessary and dilute to 100 

 ml after complete solution. Used for in- 

 numerable precipitations and microcrystals 

 of alkaloids and many related compounds 

 (generally by addition to aqueous neutral or 

 slightly acid solutions). 



Bromauric Acid Reagents 



The bromauric acid reagents as a group, 

 and HAuBr4 in H3PO4 , and in concen- 

 trated HCl, particularly, are probably the 

 most useful of all know^n reagents for micro- 

 crystal tests with compounds of basic ni- 

 trogen. 



1 g of the commercial "gold chloride" 

 (HAuCU -31120) converts to about 1.3 g 

 HAuBr4 ; dilutions of acid with water are 

 given in terms of volume of concentrated 

 acid -1- volume of water, e.g., (2 + 3)H2S04 ; 

 final volume (from 1 g of the starting ma- 

 terial) in parentheses at the end: these 

 features may be used in specifying a par- 



ticular reagent precisely, especially in places 

 where the full formula is not immediately in 

 view. 



(8) HAuBri in H.POa . HAuCl4-3H20 

 crystals 1 g, HBr (40%) 1.5 ml, H2O 1 ml, 

 syrupy H3PO4 (85-88%) 17.5 ml. Virtually 

 shows the limits of the basic quality of the 

 N atom. Used for all sorts of simple N bases, 

 feeble ones, and those partly acidic; for 

 certain inorganic cations; for oxonium com- 

 pounds; also for sympathomimetic drugs, 

 etc. (direct addition). 



(9) HAuBri in {3 -\- l)HzPOi , {1 -j- 3)- 

 HzPOa , {2 + 3)H2SOi , water, cone. HCl, 

 (1 + 3)HCl, or {2 -\- 1) acetic acid, etc. 

 HAuCl4-3H20 1 g, HBr (40%) 1.5 ml; one 

 of the media, e.g., (2 -f- 3)H2S04, to make 

 20 to 30 ml solution. In this concentration 

 especially used for addition to aqueous solu- 

 tions; for direct addition to residues of an 

 alkaloid or similar compound a greater dilu- 

 tion, to (45), or (60), may often be prefer- 

 able. Considering both aqueous and direct 

 uses, HAuBr4 in cone. HCl is perhaps the 

 best single reagent known for alkaloid-type 

 compounds. 1.3 HAuBr4 in (1 -{■ 3)HC1, 

 (45), is used especially for caffeine, theo- 

 bromine, etc. (direct addition). 



(10) 1.3 HAuBvi in 2HzP0vl{2 -f 3) 

 HiSOi, {90). Dilute 1 part of 1.3 HAuBr4 in 

 (2 + 3)H2S04 , (30)— preceding formula— 

 with 2 parts by volume of syrupy H3PO4 . 

 Used especially for the fully basic relatives 

 of amphetamine, etc. (direct addition to 

 crushed tablet material containing a salt of 

 the base). 



(11) HAuBrA in H^PO, and HBr. 



(a) 1.3 HAuBr4 in 2H3P04- lHBr,(24). 

 HAuCl4-3H20 1 g, HBr,(40%) 8 ml, H3PO4 

 16 ml. Used for methylamine hydrochloride 

 especially; also for ammonium salts, iso- 

 propylamine and diethylamine hydrochlo- 

 rides; etc. 



(b) 1.3 HAuBr4 in 9H3P04-2H20- 15HBr, 

 (26). HAuCl4-3H20 1 g, HBr(40%) 15 ml, 

 H2O 2 ml, H3PO4 9 ml. Used for ethylamine 

 and methylamine hydrochlorides, etc. 



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