PROCEEDINGS OF UNITED STATES NATIONAL MUSEUM. 131 



by Dr. Thoulet, which, though not itivented by him, was brought into 

 general notice by his more successful development of the method.^ 



In a solution of iodide of potassium, iodide of mercury was dissolved, 

 and the sp. gr. of the resultant fluid was 3.18.^ Some of the diabase 

 from Jersey City, which is particularly fresh, was pulverized till all the 

 grains would pass through coarse muslin. From this powder the dust 

 was separated by washing in water, and the mass of uniformly fine 

 grains was put into the fluid, when the iron oxide and augite sank to 

 the bottom and only feldspar remained on the top. I diluted till the 

 sp. gr. decreased to 3, when some grains of a compound character set- 

 tled out, and the microscope indicated that the floating mineral was 

 entirely of feldspar. I diluted and made the gravity 2.90, and nothing 

 of consequence fell down, neither did any considerable portion settle 

 from the mass till the sp. gr. had reached 2.69, when at this point the 

 mass of feldspar, on being mixed with the fluid as before, separated into 

 two parts with such facility as to plainly show that two minerals were 

 present. Further experiments on the i)arts did not result in any further 

 separations, and it was therefore decided to analyze these parts. These 

 analyses were performed by Dr. A. B. Howe, of the Scientific School at 

 New Haven, and were found to be composed as follows : 



FELDSPAR IN JERSEY CITY DIABASE. 



Sp. Gr. over 2.69. 



SiOz 52.84 



AI2O3 28.62 



FezOs 1.52 



CaO 11. 81 



MgO 40 



KazO 2. 38 



K2O , .86 



H2O 1. 06 



99.55 



Sp. Gr. under 2.69. 



E O : E2O3 : SiOz 

 1 1 3.3 



E2O : EO 

 1. 4.7 



It is therefore plain that the feldspathic element in this rock is not 

 any single feldspar. One of the feldspars is very plainly labradorite, 

 and the other has the ratio of andesite. The two feldspars were dis- 



have been found in small amount in some specimens. Apatite is uniformly present 

 as a minutely microscopic constituent, and the whole sequence of zeolites and chlorites* 

 with quartz, calcite, and other minerals, are present as decomposition products, but as 

 a rule it is a monotonously uniform mixture of the above three minerals. 



1 Theses pr^sent^es k la faculty des sciences de Paris, pour obtenir le grad de doc- 

 teur. Contributions h I'dtude des propri6t6s physiques et chimiques des mineraux 

 microscopiques. Par M. J. Thoulet. 



2 This result was obtained by uniting the proportions recommended by Victor Gold, 

 Schmidt, Ueber Verwendbarkeit einer Kaliumquecksilberjodidlosung, &c. Inaugural 

 Dessertation zu Heidelberg, Stuttgart, 1880. 



