544 SUMMARY OF CURUENT RESEARCHES RELATING TO 



Examination of Metalliferous Clays.— Mr. M. Atwood, in a paper 

 on the clays in the Comstock lode read before the San Francisco 

 Microscopical Socitty, describes as follows the method of separating 

 and examining the gold-bearing fragments : — 



" The way in which I made the examination of the clays was, first, 

 to place them in a porcelain di.^h, pouring hot water over and keeping 

 them in the water for several hours, stirring occasionally till all the 

 particles that would dissolve were taken up by the water. Afterwards 

 I emptied the contents of the porcelain dish into a batea, allowing 

 everything that was dissolved to float away. By the batea the pyritic 

 matter and other heavy bodies were separated from the rest of the 

 coarser, rounded, and lighter fragments of vein stuff and country 

 rock. The pyritic matter is then tested for gold, silver, and tellurium, 

 and also a microscopic examination of it is made under water. The 

 fragments of country rock and vein stuff are then washed again, using 

 a brush to rid them of any clay that might still adhere to them. 

 After drying, they are put into a separator having sieves with 30, 50, 

 and 100 hoks to the linear inch, a uniform size enabling me to 

 examine them better with the Microscope. The fragments that pass 

 through the sieve having 100 holes I place in a small cell, fastened 

 on the f^lass slide and filled with water, which I cover with thin glass. 

 The shapes of the fragments are seen much better in this way, since, 

 by slightly moving the thin glass cover, they can be made to turn 

 and exhibit their forms in diffL-reut directions." 



Microscopic Tests for Poisons.* — Professor Eossbach has pub- 

 lished, in the Vienna ' Klinische Wochenschrift,' some remarkably 

 delicate tests for the presence of poisons when they are in too minute 

 quantities to answer to any chemical tests. 



As small animals, like frogs, mice, &c., are known to be very sus- 

 ceptible to the action of certain of the poisonous alkaloids, this fact 

 is taken advantage of, and very weak solutions introduced into their 

 circulation. Delicate as the tests are as applied to frogs, &c., Pro- 

 fessor Rossbach gives far more delicate ones. A drop of water, 

 containing infusoria, is placed on a glass slide and examined un- 

 covered. The infusoria are examined carefully as to size, form, 

 colour. &c. ; then a drop of the solution is placed just at the edge of 

 the fluid containing the infusoria. If organic poisons be present the 

 infusoria are instantly destroyed, becoming a formless sediment. He 

 says ; '• If a drop of water containing infusoria and weighing • 001 

 grain be used as a test, the quantity of strychnine required to cause 

 remarkable changes will be -00000006 of a grain. In this way 

 1 of a grain of atropine can be detected." Thus, if the 



stomach of a pei-son poisoned by strychnia contains a litre of fluid 

 and only | of a grain of the alkaloid, a single drop of this fluid will 

 contain forty times as much strychnine as is necessary for the test. 



Fine Rulings. — We recently referred f to " Fasoldt's Test Plate," 

 which it was then claimed contained lines ruled at the rate of 

 1,000,000 to the inch. 

 * ''Ih- Microscope,' i. (1S81; p. 22. t See this Journal, iii. (1880) p. 891. 



