OBSERVATIONS IN CHEMISTRY AND MINERALOGY. 411 



picture developed as it is represented in fig. 4. Here a, a, designate the cupri- 

 aminosulf ate ; 6, o, the nickelotetraminosulf ate ; c, c, the praseo cobaltioctamino- 

 sulfate. The relative dimensions of the three salts are fairly true to nature; 

 the absolute dimensions are exaggerated. The copper salt is monoclinic, the 

 nickel salt is isometric (cubo-octahedrons as 6 2 , 6» and twins as 6, 60 ; they are 

 at first pale blue but soon change to pale bluish-green through lose of NH,. Th. 

 nickel salt is the most soluble of the three salts in strong ammonia. Thin 

 tabular crystals show red-purple color. The praseo cobaltisalt showB most of the 

 types and is very yellow-green. The ions of the three metals are to each other, 



by analysis: 



Cu : Ni : Co = 60 : 10 : 1. 



Sensitiveness of the Method. — Two solutions were made, one containing 

 mg. nickel per c.c. and one containing 0.5 mg. cobalt per c.c. The burette 

 containing the cobalt solution had narrow outlet and a thin edge, to that it made 

 exactly 20 sharp drops to the cubic centimeter, hence one drop contain! 0.025 



mg. Co. 



I. One drop of cobalt solution plus 2.5 c.c. of nickel solution holding 0.025 



mg. Co + 2.5 mg. Ni or Co : Ni = 1 : 100 was evaporated in a conical glass 

 tube, 2 mgs. NH 4 C1 added, and three drops of strong ammonia used for solution ; 

 one drop to slide gave cubes of nickelamino salt and with persulfate great 

 swarms of praseo burrs and chis. To make these microswarms, only 0.00s mg. C o 



was available. 



II. One drop of cobalt solution plus 25 c.c. of nickel solution holding 0.025 Co 

 and 25.0 mg. of nickel or Co : Ni = 1 : 1,000. One drop of this, containing one- 

 fiftieth of the whole or 0.0005 mg. Co and 0.5 mg. Ni, was evaporated. Residue 

 dissolved in two drops of ammonia and the whole transferred to slide gave with 

 about 1 mg. of amm. persulfate three groups of praseo crystals of the angU- 

 templet type. I should name this the safe limit of sensitiveness, though I have 

 obtained prisms or bacilli with fewer ions than correspond to 0.0005 mg. through 

 much experience in seeing and looking for the right thing in the right way. Such 

 small prisms were obtained with 0.0003 mg. Co. They measure 70 micromilli- 

 meters in length and 1 to 2 m. m. m. in width. When the whole of the evaporated 

 material of experiment II was dissolved in ammonia to purple color and a drop 

 transferred to slide very numerous crystals of the burr and chi type were formed. 



Note.— Most available samples of C. P. cobalt nitrate from reputed manu- 

 facturers gave the praseo reaction abundantly. 



Preparation and Analysis of the Praseosalt and also of tU accompanying 

 buteosaU.—lt is stated above that by the action of persulfate upon an ammo- 

 niacal solution of cobaltosalt all the known amines of cobalt can be produced: 

 the praseo and luteo amines result at low temperature, the purpureo, f usco and 

 roseo amines in warm and hot solutions. The green salt falls out first and must 

 be removed by vacuum filtration as soon as the liquid clears. The mother 



