MECHANICS AND USEFUL AUTS. 113 



lime. The oil is permitted to enter the retort and drop on the red hot apex 

 of the cone, when it is converted into gas. The gas cannot get out without 

 passing through the perforated bottom and amongst the heated mixture of 

 charcoal and lime, which tend to purify it. From the retort it passes to the 

 cooler, where it is washed with water, and from- thence into a receptacle 

 for use. 



Improvement in Gas Retorts. The object of an invention by J. G-. Hock, of 

 Newark, N. J., is to enable the heads of the retorts to be more handily and 

 quickly attached and detached than the mode of fastening them at present hi 

 general use admits. Another object is, to enable the fastening to be readily 

 detached from a worn out retort and applied to a new one. The neck of the 

 retort is cast with a strong lug on each side, close to the mouth, said lugs 

 having a square hole through them to receive the square shanks of two 

 hook headed bolts, which, with a bail and an inclined projecting rib, on the 

 outside of the retort, constitute the fastening. 



Improved Gas Burner. An improvement has been recently brought for- 

 ward designed to be used hi connection with burners where the flame is pro- 

 duced by the combustion of two jets of gas issuing simultaneously from 

 the top of the burner. The improvement consists in placing a small blade of 

 metal on top of the burners, between the gas orifices, so as to more fully 

 separate and spread the two jets, and cause the flame to be broader; the 

 metallic blade is also alleged to act as a receiver, and by becoming itself 

 highly heated, to impart additional caloric to the gas, and thus produce better 

 combustion. The blade is quite small, and the two jets unite above it in one 

 common flame, in the usual manner, excepting that it is broader and larger 

 than it would otherwise be. The invention is said to be applicable to nearly 

 ah 1 burners now hi use, and it is claimed for it that it effects an important 

 purpose, that of increasing the illuminating power of the gas without aug- 

 menting the consumption. 



KNIGHT'S SAFETY ENVELOPES. 



Mr. E. T. Knight, of Philadelphia, has recently patented an improvement in 

 envelopes for valuable and important letters, with the double purpose of 

 making the envelope, post-mark, &c., a part of the letter, and of preventing 

 any clandestine opening of the same. It is, for some purposes, quite a defect 

 in the present envelope that the gum may be moistened and the letter opened 

 without discovery. Wafers may be soaked nearly as easily, and wax is 

 liable to melt hi hot climates. In Mr. Knight's invention a little more paper 

 is used, and the flaps being locked together by a species of dovetailing in 

 addition to the gum, a metallic clasp or eyelet is put through the lower por- 

 tion near the edge, which effectually secures the whole package. An eyelet 

 through a letter folded in the ordinary manner would not only prevent its 

 removal from the envelope, but would interfere with its unfolding when pro- 

 perly opened. To avoid this difficulty the paper is to be folded with its edge 

 projecting, and this edge, rather than the folded portion, is allowed to receive 

 the eyelet. By this arrangement the soaking or tearing open of the usual flap 

 of the envelope does not release the letter, and the process required is a 



