72 



THE AMERICAN MONTHLY 



["April, 



that a specimen can be found remark- 

 able for the perfection of the crystal- 

 line forms. The perfect crystals of 

 arsenic are very beautiful when seen 

 under the microscope, and they are 

 easily obtained. An excellent method 

 of forming them on the glass slip is 

 as follows : — 



Select a small tube about one inch 

 in length, and fit it in a holder made 

 of a thin strip of copper, brass, or 

 other metal having a hole bored 

 through it to receive the tube. Let 

 the mouth of the tube project slightly 

 above the metal, and support the lat- 

 ter in some convenient way over a 

 spirit-lamp or hold it in the hand. 

 It is better to have a support. 



Place a small quantity of white ar- 

 senic in the tube, and apply heat 

 slowly until a white powder begins 

 to collect about the mouth of the tube. 

 Then warm a glass slip, and hold it 

 over the top of the tube until bright, 

 crystalline particles appear on its un- 

 der surface. Then remove the lamp 

 and let the tube cool. 



If the heat has been properly regu- 

 lated, beautiful crystals will be found 

 upon the glass slip, which give a 

 great variety of effects with different 

 illuminations. On a dark ground the 

 effects are very fine indeed. 



Cleaning Polycystina. 



The polycystina are found in many 

 localities in this country, particularly 

 in the diatomaceous rocks of Virginia 

 and Maryland ; but nowhere are their 

 remains found in such abundance as 

 in the rocks of the Bermudas and of 

 the Nicobar Islands, vv^here they form 

 strata from one to two thousand feet 

 in thickness. 



Specimens of the Barbadoes mate- 

 rial have been sent to a large num- 

 ber of subscribers, who signified 

 their desire to obtain it, as already 

 stated, and we now redeem the 

 promise to describe the method of 

 cleaning the specimens for mounting. 



The material should first be boiled 

 in a solution of washing soda, which 



will partly disintegrate it. The liquor 

 should then be poured oft' and the 

 sediment washed, allowing it to settle 

 each time before pouring off the water. 

 It should then be treated with some- 

 what diluted hydrochloric acid, which, 

 by decomposing the carbonate of lime, 

 will cause considerable effervescence, 

 and this will reduce the pieces still 

 further. Wash again, and then re- 

 peat the boiling in carbonate of soda. 



When it is thought the boiling has 

 been continued long enough to com- 

 plete the disintegration, wash thor- 

 oughly and then proceed to separate 

 the polycystina from the sand and 

 fragmentary particles, as follows : — 



Put the material in a beaker, or a 

 bottle that will hold six or eight 

 ounces. A quinine bottle is very 

 good for the purpose. Fill the bottle 

 with water and thoroughly shake it. 

 Set it on the table for thirty seconds, 

 exactly. Then pour the fluid off into 

 a larger bottle almost down to the 

 small quantity of sediment that will 

 be found at the bottom. Fill the bot- 

 tle again, shake, and let it stand thirty 

 seconds ; pour off and repeat these op- 

 erations until the water poui-s off clear. 

 This separates all the material that 

 will settle in thirty seconds. Trans- 

 fer it to a small vial and label it. 



Let the sediment deposit in the 

 large bottle, pour away the water 

 above it, transfer the sediment to the 

 first bottle, fill up with water, shake, 

 and let it stand one minute. Repeat 

 these operations as before, and thus 

 will be obtained the material that set- 

 tles in one minute. In like manner" 

 obtain what will settle in two or three 

 minutes. 



By proceeding in the systematic 

 manner above described, a large quan- 

 tity of broken particles and objection- 

 able matter will be removed, and the 

 polycystina w^ill be made tolerably 

 clean. To further clean them, take 

 the different deposits separately, and 

 proceed with each one as follows : — 

 Place it in a test-tube, and boil with 

 strong nitric acid for a moment. 

 Then wash thoroughly. After wash- 



