296 THE AMERICAN MONTHLY [Sept 



Other li(juids 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 gravity 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 

 o-ravity. — Zeitschrift fur Angewandte Mikroskopie. 



Pastes and Cements for Photographs and Other Pur- 

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

 and novelties in photographic technique, by Eder and 

 Valenta, the Drogesten Zeitung takes the following- for- 

 mulae for pastes: — 



PASTES CONTAINING STARCH. 



Gum arable 4 parts. 



Starch 3 paris. 



Sugar I part. 



Water suffieient. 

 Dissolve the gum arabic in sufficient water to take up 

 the starch; rub up together, add the sugar, and heat the 

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

 verted. 



Collodinh:.— This is simply a paste made by treating 

 starch with water rendered strongly 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 



