22 PROCEEDINGS OF THE AMERICAN ACADEMY 



After we had settled the composition of the sodic zincates, we turned 

 otir attention to the study of otlier zincates, and also tried some ex- 

 periments with magnesia oxide. The results of all this work were 

 negative, but nevertheless we think it best to give a brief statement 

 of what we have done. 



In all our attempts to prepare potassic zincate we encountered the 

 ditiiculties already mentioned by Fremy ; in fact, we have not suc- 

 ceeded in obtaining in any experiment the crystals desciibed by hitn, 

 although we have modified the process employed in a number of dif- 

 ferent ways ; but the solution of zincic oxide in potassic hydrate, when 

 treated with alcohol according to the method which had yielded such 

 good results with sodic zincate, gave only amorphous precipitates, 

 which looked like zincic oxide, but were not wholly free from potas- 

 sium ; as the absence of crystalline form left us no means by which 

 we could judge of the purity of this substance, we did not think it 

 worth analysis. 



With ammonic hydrate the results looked more promising at first, 

 as the solution of zincic hydrate in ammonic hydrate occasionally gave 

 a small quantity of crystals, after it had been mixed with alcohol and 

 allowed to stand ; but in this case there was no separation of the liquid 

 into two lavers. These crystals looked very much like the infusible 

 sodic zincate described above, but the analyses of four preparations 

 showed that they had no constant composition, the following {)ercent- 

 ages being obtained. 



I. II. lU. IV. 



Zinc 48.06 45.90 59.96 



Ammonia 7.35 4.58 3.67 5.28 



In view of these results, it did not seem worth while to continue the 

 investigation. 



In beginning this research we had hoped, by acting on the sodic 

 zincate with a cobaltous salt, to obtain Rinman's green, and in this 

 way throw some light on the composition of this pigment. These 

 hopes have not been fulfilled, as the zincates were decomposed by 

 alcohol or water, as already stated, and therefore the action could not 

 be carried on in solution, and the melted fusible zincate, when treated 

 with cobaltous chloride, gave only a blackish precipitate with no shade 

 of green. The same result was obtained when an ethereal or absolute 

 alcohol solution of cobaltous chloride was allowed to act on the zhicate. 

 We hav^e also made many attempts to purify Rinman's green, prepared 

 according to tlie usual method, in order to fit it for analysis, but none 



