Chemistry and Physics. 469 



4. A New Method for Detecting Chlorides, Bromides and 

 Iodides. — Bexedict and Snell have devised the following 

 method for the purpose under consideration: The reagents used 

 are potassium iodate of one-tenth, potassium iodide of one-fifth 

 and nitric acid of five times " molar " concentration (sp. gr. of 

 HNO3 1-18). The operations are carried out in a rather wide 

 test-tube. To the neutral solution acetic acid and KIO3 are 

 added. If iodine is thus found the liquid is boiled with addition 

 of small quantities of KIO3 until no further coloration is pro- 

 duced. To the liquid is then added nearly one-half its volume of 

 dilute nitric acid. Coloration shows bromine, which may be con- 

 firmed by shaking a portion with chloroform or carbon disul- 

 phide. The main solution is boiled until colorless, 1 or 2^'^ of KI 

 are added, and the liquid is boiled again until colorless. An 

 equal volume of concentrated nitric acid is then added together 

 with a few drops of silver nitrate solution. A white precipitate, 

 insoluble on warming, shows silver chloride. The concentrated 

 nitric acid is added to prevent the precipitation of silver iodate 

 in case there should be iodate still left in the solution after the 

 treatment with potassium iodide. When a thiocyanate is present, 

 the test for iodine is made in a portion after the addition of 

 sodium acetate. If salts of other acids are present, the silver 

 halides are first precipitated, filtered and washed, then decom- 

 posed with zinc and dilute sulphuric acid, neutralized, filtered, 

 and treated as above. The method is said to give very satis- 

 factory results, but it is evident that considerable care would be 

 necessary in making the test for iodine, since other reducing 

 agents would give the same reaction as an iodide. — Jour. Ainer. 

 Chem. iSoc, xxv, 809. h. l. w. 



5. Quartz Glass. — A very full account of the behavior of 

 this material has been given by H. Heraeus before the Inter- 

 national Congress of Practical Chemistry held lately in Berlin. 

 The history of the working of quartz was related. Experiments 

 were made as early as 1839; and the prominent experimenters in 

 the subject have been Gaudin, Gautier, Boys, Dnfour, Hutton, 

 Shenstone, and, also, Heraeus. 



The chemical relations of quartz are especially interesting. 

 Quartz vessels are unaffected by water, acids and &;alt solutions ; 

 but are affected by alkaline fluids. At high temperatures all 

 oxides are dangerous for the vessels. One therefore should care- 

 fully clean such vessels; and abstain from touching them with the 

 fingers. If one encloses a quartz tube in an electric furnace and 

 heats it for several hours to about 1300°, its surface remains 

 clear and limpid when it is taken out of the furnace. With a 

 microscope, however, one perceives a slight change of the surface; 

 when it cools sufiiciently to be taken by the hand the whole sur- 

 face becomes quickly clouded and non-transparent. Heraeus 

 attributes this to a vitrification of the amorphous silicate and is 

 a surface action. When this experiment is repeated in a closed 

 platinum cylinder no such silicate is formed- At high tempera- 



