PROCEEDINGS OF UNITED STATES NATIONAL MUSEUM. 131 



by Dr. Thoulet, which, though not invented 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 iluid 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 

 Avas 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 (iiluted 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, aud nothing 

 of consequence fell down, neither did any considerable portion settle 

 from the mass till tbe sp. gr. had reached 2.G9, 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 jdainly show that two minerals were 

 present. Further cxi^eriments on the parts did not result in any further 

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

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

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



FELDSPAR IN JERSEY CITY DIABAST5. 



Sp. Gr. over 2.G9. 



SiOa 52.84 .88 



ALO3 18.02 .278 



FczOa 1.52 .009 



CaO 11.81 .21 



MgO . 4G . 01 • 



NajO 2. 38 .038 



K2O .86 .009 



H2O l.OC 



Sp. Gr. under 2.09. 



SiO. 00. 54 



AI2O3 24. 11 



99.55 



E O : E.O3 : SiOa 

 1 1 3.3 



E2O : 110 

 1. 4.7 



Fe^Oa 

 CaO 

 MgO . 

 Na^O. 

 K2O . 

 H2O., 



1.14 

 9.15 



.27 



, 4.11 



1.00 



.59 



100. 97 



01 



::34 



007 



103 



107 



000 



Oil 



E O : E2O3 : SiOa 

 1 90 4.09 

 E2O : E O. 



1. 2.2 



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 foiiud in small amomit iu some specimens. Apatite is uniformly present 

 as a minutely microscopic constituent, and the wliole sequence of zeolites and chlorites- 

 ■\vith quartz, calcitc, and other minerals, are present as decomposition products, but as 

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



' Theses pr^sent6es h la faculty des sciences de Paris, pour obtenir le grad de doc- 

 teur. Contributions a I'etude des propri^tes i)hysiques et chiniiques des mineraux 

 microscopiqnes. Par M. J. Thoulet. 



-This result was obtained by uniting the proportions recounueuded by Victor Gold, 

 Schmidt, Ueber Verwendbarkeit eiiier Kaliumquecksilberjodidlosung, &c. Inaugural 

 Dessert ation zu Heidelberg, Stuttgart, 1880. 



