1885 - 12th Avenue each other in a number of different ways by the chemist. Hardness is one of the factors sometimes resorted to. This may be accomplished by attempt- ing to scratch materials of varying de- gree of hardness, until one is found that can be scratched by the piece of glass under test. The other sample is then tested in similar manner, and the results compared. Specific Gravity is an important factor. This is the relative weight of the glass to the weight of an identical volume of water. It can be accomplished by the well known displacement test in a specific gravity bottle. However the chemist uses a much more refined technique. There is also the Refrac- tive Index of the glass which had to be taken into consideration. This is the ability of the glass to bend a ray of light. It may be roughly determined by placing the glass fragments in a bottle with a liquid of a known refrac- tive index close to that of glass gen- erally. The glass pieces can still be seen in the bottle. Then a second liquid with a different refractive in- dex is carefully added, little by little until the glass seems to disappear. This will indicate that both the glass and the liquid have the same refrac- tive index. By computing the relative amounts of the two liquids used in making the test, the refractive index of the glass is obtained. In actual practice, however far more accurate methods are employed by the chemist as he determines the refractive index of the sample under test to four decimal places. Fluorescence is also sometimes taken into consideration. The glass is subjected to ultra violet light. Different components in the elass vary the intensity and color of the fluorescence. If two samples do EUROPE eee FULLY LICENSED Modern Rooms Hot Water Heated A Home Away From Home SERVICE WITH A SMILE PRINCE GEORGE B.C. TWENTY-SIXTH EDITION Manufacturers and Wholesalers of + + + not show the same degrees of color of fluorescence, then they can be readily eliminated. Last, but certainly not least, is the Spectographic Analysis of glass. The chemical composition of the glass is definitely ascertained by this method, even to traces of im- purities which might be present in the original ingredients. The percentages of the different components can also be measured. To put it simply, the spectrograph vaporizes a tiny frag- ment of glass in an electric arc. The light emitted from the glass vapours is then broken up into a spectrum and photographed. By comparing known standards with the photographic nega- tive both a quantitative and qualita- tive analysis is made at the same time. These tests are applied to both samples and the results compared. By these means the Analyst can definitely tell whether or not two samples of glass are identical in all respects. To illustrate the diversity of com- ponents and impurities found in specimens of glass, is the following list: — Major constituents— Lime Soda Potash Silica Lead Barium Boron Beryllium Zinc Thalium Minors and impurities— Iron Aluminum Arsenic Managanese Strontium Magnesia Chromium Molybdenum Copper As there is so little generally known about the subject of glass fractures, perhaps a digression from the original All Comrades Are Welcome At Branch No. 43 Canadian Legion, B.E.S.L. Corner Quebec and 5th Ave. * William Duncan, Secy. * PRINCE GEORGE B.C. J. H. Bond, Pres. ALLEN LUMBER CO. LTD. SPRUCE, FIR and PINE DRESSED LUMBER PRINCE GEORGE, British Columbia EMBASSY CAFE Chop Suey and Chow Mein A SPECIALTY * PRINCE GEORGE B.C. NECHAKO BAKERY QUALITY BAKERY PRODUCTS * Box 301, Phone 55-R-1 PRINCE GEORGE B.C. COMPLIMENTS OF... NATIONAL CAFE PRINCE GEORGE B.C. Patronize the Advertisers SHIELDS MOTOR PRODUCTS Ltd. GENERAL MOTOR PARTS SALES and SERVICE * PRINCE GEORGE B.C. La Pointe Bros. Limited Manufacturers of Spruce and Pine Lumber x P.O. Box 505 PRINCE GEORGE Page Fifty-nine