296 THE AMERICAN MONTHLY [Sept 



Other liquids are: Silver iodide dissolved in concentrated 

 solution of silver nitrate, which makes an oily, brown 

 liquid of s. g"., 5.00. Thallium-silver nitrate, melting- at 

 75 C, s. g-., 4.1. Concerning- this last named chemical the 

 Bayerische Industrie und Gewerbeblatt has the following- 

 information: 



The specific g-ravity and the melting- point of thallium- 

 silver nitrite fall as the proportion of thallium nitrate is 

 increased, thus, while the latter substance has a specific 

 gravity of 5.00, and a melting- point of 250, the addition of 

 1 part of silver nitrate to 4 parts of the thallium salt 

 decreases the melting- point to 200 deg-rees C, and the s. g-., 

 to 4.9. Three parts of silver nitrate to 4 parts of thallium 

 nitrate bring- the s. g-. down to 4.7 and the melting- point to 

 100 degrees C. 



All the above are soluble in, or miscible with water in 

 every proportion. In using- them the material is thrown 

 on the liquid, and floats or sinks according- to its specific 

 g-ravity. — Zeitschrift fur Ang-ewandte Mikroskopie. 



Pastes and Cements for Photographs and Other Pur- 

 poses. — From a recent publication on the recent prog-ress 

 and novelties in photog-raphic technique, by Eder and 

 Valenta, the Drogesten Zeitung- takes the following- for- 

 mulae for pastes: — 



PASTES CONTAINING STARCH. 



Gum arable 4 parts. 



Starch 3 parts. 



Sugar I part. 



Water sufficient. 



Dissolve the gum arabic in sufficient water to take up 

 the starch; rub up tog-ether, add the sug-ar, and heat the 

 whole on a water-bath until the starch is completely con- 

 verted. 



CoLLODiNE. — This is simply a paste made by treating- 

 starch with water rendered strong-ly alkaline, whereby the 

 substance is rendered soluble. 



Triticine. — This is a paste made of dextrin and starch 

 in equal parts, in water, the starch being- made soluble by 



