REAGENTS FOR MICROCRYSTAL IDENTIFICATIONS 



and crystals with ammonia and the lower 

 amines. 



(22) Reinecke salt, NHiCr{NHs)2{SCN), . 

 A fresh, approximately saturated, aqueous 

 solution is used. Stir a little of the com- 

 pound into about 0.5 ml water at room tem- 

 perature, to provide a few drops for use. 

 Properties of the reagent begin to change 

 within a few hours. Rosenthaler says that it 

 is useless when the ferric salt test for thio- 

 cyanate ion can be obtained (red color). 

 Some very interesting crystals with lower 

 amines have been obtained with a still- 

 effective reagent aged for a number of hours 

 — e.g., overnight — but the writer does not 

 know how to control these changes or sta- 

 bilize any such intermediate stage. Gradu- 

 ally, in two or three days, effectiveness is 

 completely lost. 



Bromine-Bromide Reagents 



Although various forms of bromine- 

 bromide reagents should be possible and 

 valuable (as with iodine-iodide), the diffi- 

 culty of keeping any reagent without the 

 bromine evaporating, and its disagreeable 

 character, have so far prevented anything 

 but a limited aqueous use. 



(23) Br in HBr solution; Br in NaBr 

 solution. HBr(40%) 10 ml, water 90 ml; 

 or NaBr 5 g, water 100 ml. Saturate with 

 bromine. Used for barbiturates, etc., as well 

 as for basic compounds. 



Other Reagents for Aqueous Tests 



The following are added to aqueous solu- 

 tions (usually of a salt of the base tested), 

 unless otherwise stated. 



Complex Oxygen Acids. (24) Phosphori- 

 timgstic acid. Obtainable commercially. 10 g 

 in 100 ml water. Sihcotungstic acid is used 

 similarly. 



(25) Phosphorimolyhdic acid with HNO?, . 

 10 g of the commercial phosphomolybdic 

 acid in 90 ml water and 10 ml coned HNO3 . 

 Phosphorimolyhdic acid has especial value 

 as a standard for sensitivity determinations. 



Formerly the reagent for this purpose was 

 made with only a few drops HNO3 ; but 

 there is probably no sufficient reason to 

 maintain a separate formula for it; the 

 form with 10% HNO3 may be better for 

 crystals as well as being used foi- the follow- 

 ing reagent. 



(26) Phosphorimolyhdic acid with H^POi . 

 A fresh solution of the commercial phospho- 

 molybdic acid is decolorized immediately by 

 H3PO4 , but the preceding solution with 

 HNO3 , after standing at least 6 weeks, is 

 more stable. To 4 ml of the stabilized yellow 

 phosphorimolyhdic acid add 0.6 ml syrupy 

 H3PO4 and mix. The solution should remain 

 yellow for use (it will keep for a few days). 

 Less sensitive but gives crystals (e.g., with 

 narceine and atropine) which are unobtain- 

 able with the usual phosphorimolyhdic r.cid 

 solution. 



Platinum and ^lercury Thiocyanates. 

 (27) H^PtiSCN), . H2PtCl6'-6H20 I'g, water 

 20 ml, NaSCN 0.95 g. This hardly has out- 

 standing importance for microcrystals so 

 far, but probably is the best of the "normal" 

 thiocyanates (i.e., aside from Reinecke salt); 

 and the writer takes this opportunity of 

 correcting a former statement that onh- 

 about a third as much NaSCN need be used : 

 the NaSCN must be sufficient to replace all 

 six CI atoms, or the reagent will precipitate 

 on standing. 



(28) K2Hg{SCN)i. Dissolve 3 g KSCN 

 in 100 ml water and saturate with Hg(SCN)2 

 (5 or 6 g recjuired). This is an outstanding 

 reagent for inorganic microcrystals of a num- 

 ber of cations, especially Zn, Cd, Cu, Co, 

 and Au. It precipitates alkaloidal-type com- 

 pounds but its value for this is minor. 



Mercuric Iodide Reagents. (29) KoHgli. 

 Dissolve 2 g KI in 100 ml water and saturate 

 with Hgl2 (nearly 3 g Hgl2 required). Only 

 occasional value for crystals but much used 

 for general tests of alkaloid-type precipita- 

 tion. 



(30) Hglo and HCl. Dilute 27 ml cone. 

 HCl to 100 ml with water (makes an actual 



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