16 TESTING MISCELLANEOUS SUPPLIES. 



requiring that a certain fraction should distil between specified temperatures. 

 To make this determination distil 100 cc in a round-bottom flask 6.5 cm in 

 diameter ; the neck should be 1.6 cm in diameter and 15 cm long, with a side 

 tube set in the middle of the neck at an angle of 75. The surface of the 

 liquid should be 9 cm below the side tube, and the bulb of the thermometer 

 just below the side tube. 



6. Benzol. 



Mix the sample with 8 volumes of strong sulphuric acid and 2 volumes of 

 nitric acid; heat gently for ten minutes, allow to cool, and note odor. The 

 odor of nitrobenzol indicates benzol. 



7. Color and Odor. 

 Note color of sample and odor both in bulk and after rubbing on hands. 



DRY SHELLAC. 

 1. Detection of Rosin (Liebermann-Storch Test). 



To 1 gram of the sample add 15 cc of acetic anhydrid, heat gently until solu- 

 tion is complete, cool, draw off the acetic anhydrid, and add a drop of sul- 

 phuric acid 1.53 specific gravity. A fugitive violet color indicates rosin. 



2. Determination of Rosin (Langmuir's Method). 



To 0.200 gram of ground shellac, in a 250 cc dry bottle of clear glass with a 

 well fitting ground glass stopper, add 20 cc glacial acetic acid, and warm gently 

 until the shellac is dissolved (a little shellac wax will remain undissolved, and 

 at least half an hour should be allowed, for the shellac itself is difficultly solu- 

 ble). Then add 10 cc of chloroform and cool the solution down to 21 to 24 C. 

 Add 20 cc of Wijs' iodin monochlorid solution, shake, and keep in the dark at a 

 temperature between 21 and 24 C. for one hour, add 10 cc of potassium iodid 

 rotation, and titrate immediately with thiosulphate 25 cc may be run in at 

 once and the remainder gradually with vigorous shaking, adding starch solu- 

 tion Just before the end. The end point is sharp; any color returning after 

 half a minute or so may be disregarded. If less than 25 cc thiosulphate is 

 required reject result and repeat determination, using a smaller quantity of 



The \Vija solution may be made either by dissolving iodin monochlorid in glacial 

 acetic acid or by dissolving iodin in glacial acetic acid and passing in dry chlorin 

 until the halogen content (figured as iodin) has nearly doubled; there may be 

 a very slight excess of iodin, but there must be no excess of chlorin above 

 the theory for Iodin Hilm-id. The halogen content figured as iodin should be 

 :i I H.I n is grams per 1,000 cc. The glacial acetic acid used must be free from 

 n-.lu. in- snhstMiHvs and have a melting point between 14.7 and 15 C. The 

 tltioHulphate solution should he a decinormal sodium thiosulphate solution. 

 The potassium iodid solution is 10 per cent. Blanks must be run each time 

 and the iodin number calculated from the difference between the titration result 



on the Hunk <>n the sample. Calculate the per cent of rosin, using the formula : 



^1 _ ft 

 y=100 y |/ . where y=per cent rosin, M =Iodin number of shellac, 2V r =iodin 



number of rosin, and A=iodin number determined. 



J. Soc. Chern. Ind., 1905, 24 : 12-17. 



