and Laboratory Methods. 2053 



as the case may require. The complete control of the organs of locomotion 

 and of the mouth parts, thus easily obtained, will be appreciated by many who 

 are engaged in research work. A valuable characteristic of Chloretone is that 

 it does not, in most animals, produce contraction of the muscles, but they remain 

 limp and expanded. It is extremely useful, therefore, alone or followed by a 

 killing agent in the preparation of well expanded museum and laboratory speci- 

 mens. The time required for inducing the hypnotic state or complete anesthesia 

 varies widely in different species, depending, apparently, on the absorbing power 

 of the general surface of the body and gills, if the latter are present, the observed 

 minimum being fifteen seconds in large, active amcebae and the maximum forty- 

 five minutes in a medium-sized crayfish. A. H. Cole. 



University of Chicago. 



MICRO-CHEMICAL ANALYSIS. 

 XX. 



SILVER GROUP CONTINUED— LEAD. 



V. In the presetice of a salt of Copper ami of Potassium Nitrite, Lead forms 

 a Triple A'itrite of Fotassiutn, Copper and Lead of low solubility. 



Pb(N03),+Cu(C.,H302)2+6KN02=[2KN02.Cu(N02)2«Pb(N02)2] + 



2KNO3+2KC2H3O2. 



Method. To the moderately concentrated neutral test drop add a trace of 

 acetic acid, then a fragment or two of sodium acetate and of copper acetate. 

 Stir. Then add a fragment of potassium nitrite. In 

 a few seconds cubes and squares and rectangular plates 

 separate which are brown by reflected light, jet black 

 by transmitted light (Fig. 84). Very thin plates appear 

 brown by transmitted light. 



Reinarks. This reaction is an extremely interest- 

 ing and valuable one, though in the form described is 

 not so delicate as some of the other tests for lead. If, 

 however, we add to the test drop after the nitrite has 

 been introduced a very little cesium chloride, a triple 





nitrite of cesium, copper and lead results whose solu- »p'w.--o.o»w«v 

 bility is much lower than that of the corresponding Fig. 84. 



potassium salt, thereby increasing the delicacy of the reaction. It is possible to 

 carry the limit of the reaction yet farther by substituting for the cesium chloride 

 a little thallous nitrate, the test now becomes the most delicate micro-chemical 

 test for lead which we now possess. Owing to the very low solubility of this 

 triple nitrite of thallium, copper and lead the crystals obtained are always 

 very small and require a high power to resolve them into black cubes and rec- 

 tangular plates. 



This test is a most convenient one if alloys or substances suspected of con- 



