486 M. C. Lea — Nature of Certain Solutions 



In a Griffin's beaker place 100 co of alcohol of 95 per cent 

 add 5 grams of quinia sulphate and 40 cc of acetic acid of 50 

 per cent. Take dilute sulphuric acid containing one-tenth by 

 weight of acid and add of this 7 CC . Place the beaker in a 

 water bath and apply heat till the alcohol begins to boil gently, 

 then add with constant stirring 20 oc of a ten per cent solution 

 of iodine. Turn off the heat, cover the beaker with a glass 

 plate and allow it to cool slowly with the bath. Next day 

 throw the crystals on a filter and wash with TO per cent alco- 

 hol. Press between blotting paper and dry at ordinary temper- 

 ature. 



Herapathite appears to be a very permanent substance. 

 Some that I prepared over thirty years ago has been kept in a 

 stoppered but not sealed white glass bottle and freely exposed 

 to light during this time. It appears to be quite unchanged 

 and was used in part of the work just described. 



In preparing the test solution time is gained by using the 

 barium carbonate in considerable excess and by frequent shak- 

 ing. The herapathite should be in tine powder. After the 

 green particles have entirely disappeared, which will usually 

 take a day or two, the solution must be filtered off and be 

 placed in contact with a fresh portion of barium carbonate 

 with frequent shaking for several days. The complete re- 

 moval of the last traces of sulphuric acid cannot be judged of, 

 as might be supposed, by allowing a portion to evaporate and 

 examining for the crystals of herapathite. A specimen may 

 dry up to a yellow varnish and yet may contain sulphuric acid 

 as may be shown by evaporating to dryness with a little 

 ammonia, exhausting the residue with very dilute hydrochloric 

 acid and adding a drop of barium chloride solution. But 

 there is a very much simpler and at the same time more effec- 

 tive means of testing. A solution is allowed to evaporate 

 spontaneously after adding a drop or two of solution of oxalic 

 acid. Then if there is the slightest trace of herapathite 

 present it will show itself in extremely characteristic crystals, 

 either small rosettes of black prisms or in thin light brown 

 transparent plates which are black when crossed. A great 

 many acids have this property of forcing out a crystallization, 

 for example acetic, citric, tartaric, malic and even arsenic. On 

 the other hand hydrochloric, hydrobromic and nitric acids 

 have not this power. 



The explanation appears to be this. Iodoquinia is a colloid 

 and when present in large excess is able to prevent the crystal- 

 lization of the relatively small proportion of herapathite 

 present. The addition of either of the first named series of 

 acids appears to convert the colloid base into a crystalline salt 



