ALKALOIDS AND ALKALOIDAL-TYPE PRECIPITATION 



(e.g., FeCls). These were more or less assimi- soluble in H3PO4 tliaii in water, and far 

 lated to the ordinary aqueous reagents; but more soluble in acetic acid than in water, 

 some 20 or 25 % of concentrated HCl in the The reagents with acetic acid are therefore 

 reagent will profoundly affect the precipi- less general than others, and find their espe- 

 tation and crystal-forming 'properties of cial application with highly complex com- 

 HAuCls , for example. Next, reagents made pounds, very easy to precipitate, particularly 

 with concentrated HCl were tried; then in- those that yield only amorphous precipitates 

 stead of using only aqueous solutions of the in the conventional tests. Instead of having 

 substance tested, concentrated HCl was also to study new precipitating agents which are 

 used for this purpose The value of other less and less general in effect, we can simply 

 acids was later discovered. It became evi- try using acetic acid in the test-drop, as a 

 dent that instead of dissolving the substance medium for new, useful tests. 

 tested in quite a number of different acids, The effect of phosphoric acid in increasing 

 it would be simpler to apply the reagents, the range of the tests is even more impor- 

 in the various acids, directly to a Httle tant. There are in fact three effects. One is 

 of the solid substance. This is now the the effect of a nonvolatile liquid medium in 

 method used, but precipitati^on from solution allowing a test to stand as long as may be 

 could be used. The precipitating agents are desired for crystallization to occur. H3PO4 

 the same ones that have long been used in has no very strong tendency to absorb water, 

 aqueous solution to precipitate alkaloids. nor, when it is used already a little diluted, 

 The acids proved to have very different to dry out. It has no side effects correspond- 

 effects. The ones chiefly used are diluted or ing to sulfonation, or to the withdrawal of 

 syrupy (85-88 %) H3PO4 , diluted H2SO4 , water from the molecule of a dissolved sub- 

 concentrated HCl, and (2 + 1) acetic acid, stance, both often given by H2SO4 even when 

 Concentrated H2SO4 would react with too it is somewhat diluted. Another effect is 

 many of the substances to be tested, and that of any strong mineral acid in suppress- 

 would decompose nearly all precipitating ing acidic qualities of amphoteric substances 

 agents, but may be used up to (1 + 1) and enhancing their basic qualities Third 

 strength with chloride reagents, as strong as and especially important is the particular 

 (2 + 3) with bromides, and up to (1 + 3) effect of phosphoric acid in increasing the 

 with iodides. Acetic acid may be used up to insolubility of precipitates in it, as already 

 the glacial strength except that it then tends mentioned. 



to creep and spread all over the slide, and The most useful of all the crystal-produc- 



for this reason (2 + 1) is usually the maxi- i"g compounds are the chloro- and bromo- 



mum strength employed. ^^^^^ «^ ^'^^^ ^^^.^ platmum, the iodide re- 



^-r -J. ■ r J ^T_ i XT- • -^ i- agents of platinum and bismuth, and 

 Now it IS found that the precipitation- . ^,. ^,^ ^ . ,. ^^^ , ,' , 

 „» , . , ,,!•«. .- 1-, . 1 TT o/-i lodme-KI or lodme-Hl. Among other ad- 

 eft ect is not greatly different in diluted H 2^04 , ,, 11 , 1 J ^1 



, ^^_, ^ .... vantages these are all colored, and crvstals 



or m concentrated HCl from that in plain ^ ji.i u j-ij-^- "^-uj 



^ formed by them can be readily distinguished 



water, only a little greater m diluted H2SO4 ^^.^^^ ^^.^.^^^^ crystalline material, or from 



and a little less m concentrated HCl; and ^lystals, e.g., phosphates, formed simply by 



these acids are chiefly used, as media, to ob- ^^le acid used. They are compatible, with 



tain certain crystallization effects not ob- proper formulas, with all the acids men- 



tainable in plain water. The most surprising tioned, and extend the use of microcrystal 



effects are obtained with phosphoric and tests for identification to all compounds of 



acetic acids. The compounds formed by the basic nitrogen. Phosphoric acid reagents in 



precipitants with bases are immensely less particular are used for relatively simple, and 



19 



