642 Jamieson — Polythionic Acids. 



liberated for some time after bringing the constituents 

 together. 



The following experiments were made : 





Na a S 2 3 .5H 2 



K2S2O6 



Na 2 S 2 3 .5H 2 





tfo. 



taken 



taken 



found 



Error 



1 



•0616 







•0615 



— -oooi 



2 



•0616 



0-50 



•0615 



— -oooi 



3 



•1233 



1-00 



•1230 



— -0003 



4 



•1849 



TOO 



•1851 



+ -0002 



These results show that the dithionate does not interfere 

 with the titration of the thiosulphate. 



Sheffield Chemical Laboratory, 

 Yale University. 



Art. XLV. — Datolite from Great Notch, New Jersey • by 

 C. W. Cook and E. H. Keaus. 



During the past summer the Mineralogical Laboratory of 

 the University of Michigan obtained from the Ward's Natural 

 Science Establishment of Rochester, ~N. Y., a number of 

 crystal specimens of datolite, from Great JSTotch, N. J. 

 Although these crystals show no new forms, they seem worthy 

 of description on account of their very interesting and unusual 

 type of development and the fact that they show a selective 

 coating. The specimens consist of both isolated crystals and 

 crystal aggregates, the individual crystals ranging from 3 mm to 

 35 mm in their major diameter. 



Crystallography. — On account of the coating which covers 

 most of the faces of the crystals accurate measurements were 

 difficult and in some instances impossible. A number of the 

 forms shown in fig. 1 have therefore been determined by their 

 zonal relationships. However a sufficient number of the faces 

 were identified by goniometric measurements to insure the 

 proper orientation of the crystals. On account of the imper- 

 fection of the faces in general, no attempt was made to 

 establish an axial ratio. Maintaining the stand taken in an 

 earlier paper on datolite,* the authors have assumed the posi- 

 tion adopted by Levyf and Dan a, J and which has recently 

 been championed very strongly by lJngemach.§ 



* Datolite from Westfield, Mass., this Journal (4), vol. xxii, pp. 21-28, 

 1906; Zs. Kryst., xlii, pp. 327-333, 1906. 



+ Description d'une collection de mineraux, etc., pp. 179 and 182, 1838. 

 X System of Mineralogy. 6th edition, 1892, pp. 504-505. 

 §Zs. Kryst., xlix, pp. 459-476, 1911. 



