Cutting of Steel by soft Iron. — Purple Tint of Plate Glass. 317 



Tenthredo of modern entomologists, or to the Linnsean genus, 

 which constitutes their family Tenthredinidcc, including 23 Bri- 

 tish genera, according to Dr. Leach's division, as given in 

 Mr. Samouelle's Entomologist's Compendium. 



CUTTING OF STEEL BY SOFT IRON. 



Mr. Barnes, of Cornwall, Connecticut, has ascertained a 

 singular property of soft iron in cutting hard steel. He had 

 fixed a circular plate of soft sheet iron on an axis, and putting 

 it into a lathe, gave it veiy rapid I'otatory motion, applying, 

 at the same time, a file to it to make it perfectly round and 

 smooth ; the file, however, was cut in two by the plate, the 

 latter remaining untouched; and it was found not to have 

 been much warmed in the operation, though a band of intense 

 fire surrounded it whilst in action. 



A saw made of a very hard plate, which required altering, 

 was cut through longitudinally in a few minutes, and after- 

 wards teeth were cut in it by the same means. Had the file 

 been used to produce the same effect, it would have required 

 a long and tedious operation. 



Rock crystal applied to the plate cut it readily. — SiUiman's 

 Jour. vi. 336. 



Mr. Jacob Perkins, of Fleet- street, has verified this remarkable 

 and useful observation. A piece of a large hard file was cut by 

 him into deep notches at the end, where, also, from the heat 

 produced by friction, it had softened and been thrown out like 

 a bur. On another part of the file, whei'e the plate had been 

 applied against its flat face, the teeth were removed, witiiout 

 any sensible elevation of the temperature of the metal. The 

 plate, which had previously been made true, was not reduced 

 either in size or weight during the experiment, but it had, ac- 

 cording to Mr. Perkins, acquired an exceeding hard surface 

 at the cutting part. — Journal of Science, xvi. 155. 



PURPLE TINT OF PLATE GLASS AFFECTED BY LIGHT. 



" It is well known," Mr. Faraday remarks, " that certain 

 pieces of plate glass acquire, by degrees, a purple tinge, and 

 ultimately become of a comparatively deep coloui-. The 

 change is known to be gradual, but yet so rapid as easily to 

 be observed in the course of two or three years. Much of 

 the plate glass which was put a few years back into some of 

 the houses in Bridge-street, Blackfriars, though at first co- 

 lourless, has now ac(|uired a violet or purple colour. Wish- 

 ing to ascertain whether the sun's rays had any influence 

 in producuig tliis change, the following exjieriinent was made : 

 Three pieces of glass were selected, wliich were judged ca- 

 pable 



