Proceedings of the Polytechnic Association. 721 



column, under the condition of equilibrium, will be inversel}'^ as 

 their densities. Two glass tubes, communicating with each other at 

 the bottom, are placed side by side with a graduated scale between 

 them. One tube is connected with the feed-water, and the other 

 with the water in tlie boiler ; so arranged that when the comparison 

 is to be made the connections are cut off. It is said the accuracy of 

 this apparatus permits a nearer approach to the point of saturation 

 than formerly, thus obviating the difficulties and loss of heat arising 

 from a too frequent extraction of the saline deposits from the boiler. 



Mica Spectacles. 



A device, simple for the protection of the eyes of persons engaged 

 in working metals, is one of the results of an investigation by Dr. IT. 

 Colin, an occulist of Breslau. His inquiries extended to six manu- 

 facturing establisliments, embracing 599 fitters, 386 blacksmiths, 129 

 turners, thirty-five drillers, thirteen planers, twenty-seven engine- 

 wrights, five screwers, fifteen boiler-makers, sixty-nine founderymen, 

 eiglit cleaners of castings ; total, 1,283. He found that ninety per 

 cent of tlie workmen had often been injured on the eye by minute 

 pieces of metal, and that forty-nine per cent had been under medical 

 treatment for serious accidents to their eyes. Of the wliole numlier, 

 fifty-nine were found to be permanently injured, and twenty-one of 

 those had each lost the use of one eye. The whole time lost by the 

 workmen from accidents to the eye amounted to 4,Y26 working 

 days. Ko protection to the eye had been provided. Ordinary glass 

 spectacles were (objected to on account of their liability to be broken. 

 At the suggestion of Dr. Cohn mica spectacles were tried, and found 

 to fulfill all the requirements. The mica used is of the purest kind,, 

 about half a millimeter in thickness, and is curved somewhat like 

 watch glass It is held in a frame which fits close to the side of the 

 eye, so as to prevent the entrance of particles on either side. Mica 

 imparts a pale grey tint to objects, but does not impair the eye. Its. 

 toughness, elasticity and transparency admirably adapt it to the pro- 

 tection of the eyes of metal workers. The price of a pair of mica 

 spectacles at Breslau is about fifteen cents. 



Process for Bleaching Palm Oil. 



M. Engelhardt, of Leipzig, rapidly bleaches palm oil in the follow- 

 ing manner : The oil is heated in a cauldron to about 144 degrees 

 Fahr., and allowed to remain during one night. On the following day 



[Ikst.] 46 



