620 Transactions of the American Institute. 



chromium steel is one of the stoutest kinds of steel existing. The 

 superintendent of the great bridge, building at St. Louis, has made 

 experiments upon the strength of different kinds of steel ; and he 

 found that heavy bars of steel did not come up to the standard. For 

 instance, taking a bar of steel of one square inch section, which would 

 bear a tensile strain of 100,000 pounds, it was found that a bar of 

 steel, of six or eight square inches section, would not bear a strain in 

 proportion. Their bridge is to be of the same character as that of 

 Louisville, upon the same system of girders which have to stand both 

 pressure and expansion. It is found that chromium steel will not 

 only bear 140,000 pounds for a bar of a square inch section, but that 

 a bar of eight square inches section will bear eight times that strain. 

 It has been decided, therefore, to build the St.vLouis bridge of chro- 

 mium steel. I have become acquainted recently with parties making 

 silicic steel. It was to be expected that silica might take the place 

 of carbon in steel ; but that chromium could t ike the place of carbon 

 was unexpected. Sulphur or phosphorus in iron injures it, making 

 it cold-short ; but chromium, carbon and silicon improve it. 



The oxide of chromium is the substance with which. our greenbacks 

 are printed. It is not so bright as green produced with prussian blue, 

 but it cannot be changed chemically. 



Dr. Feuchtwanger — That is the reason I rmtde ink of it. It makes 

 a good black ink, with a greenish tinge. 



Dr. Yan der Weyde — The bichromate of gelatine has the peculiar 

 property of being soluble in the dark, but when exposed to the light 

 it becomes insoluble. Coating a plate with it, and putting it under a 

 negative, wherever the sun strikes it, it makes it insoluble, the solu- 

 bility being in proportion to the amount of light. After it has been 

 exposed two or three minutes, it is carefully washed with warm 

 water, and that which is still soluble is washed away, leaving the 

 picture in relief upon the plate. In this way the Albertype is made, 

 and any number of copies can be printed. 



The bichromate of potash was introduced for use in batteries by 

 Messrs. Chester in this city, under the name of the Electropoion fluid. 

 When it is used in a battery, there are no fumes at all, because the 

 product is chrome alum, an alum in which chrome-oxide replaces 

 alumina. 



Chrome yellow is often adultered with chalk. The test of its 

 purity is to determine how much blue may be mixed with it, and 

 form a green. If there is much white in it, it will not make a good 



