608 TRANSACTIONS OF THE AMERICAN INSTITUTE. 



as vegetable oils, only after losing about 25 per cent of their 

 weight by distillation. Violette's experiments show that these 

 resins, heated in a closed vessel at a temperature between 350 and 

 400° G, or 662 and 752° Fahr., acquire after cooling, without losing 

 any of their weight, the property of dissolving, hot or cold, in the 

 above named liquids, and forming excellent varnishes. He finds 

 also that Copal resin, heated as stated, under pressure, with one 

 third of drying linseed oil and one-third of essence of turpentine, 

 gives directly, without loss, a rich, clear limpid varnish of a beau- 

 tiful slightly lemon color, perfectly adopted for carriages, and for 

 the inside as v/ell as the outside of rooms, where delicate painting 

 is required. Under the double influence of heat and pressure this 

 resin acquires new properties. Manufacturers who Avould take 

 advantage of this discovery, must bear in mind the retort used 

 will be subject to a pressure of at least 300 lbs. to the square inch. 



Np:av Inventions. 



Dr. J. B. Rich exhibited a new screw wrench, which he had tested 

 and found to be a valuable invention. It could be adjusted while 

 in use with one hand, and he thought it was the most convenient 

 tool of the kind he had ever seen. 



Mr. Buchanan exhibited an electrotyped embossing stamp, 

 which was favorably spoken of. 



The new water-proof letter envelope, used at the United States 

 Patent office, was also shown ; it is made of paper coated with 

 India rubber varnish. 



Gold Dredger. 



Mr. J. Johnson, of Saco, Maine, exhibited a model of his ap- 

 paratus for dredging rivers for gold, which he intended to put in 

 practical operation in one of the livers of Georgia. It consists of 

 a centrifugal pump, connected Avlth a pipe long enough to touch 

 the bottom of a river, while the pump w\as operated by steam on 

 a boat. He thought that almost every new substance found on the 

 bottom of a river could be brought up. He showed by experiment 

 that -weight was no obstable, it merely impeded the speed. 



Mr. J. K.' Fisher suirgested that a similar apparatus might be 

 used for cleaning city sewers. 



Mr. W. Lee said he had used for years a similar method in 

 searching the bottom of the sea for sunken treasure. His prin- 

 cipal experiments were made in the Bhick Sea, in the harbor of 

 Sebastopol. He found that the centrifugal pump drew up every 

 thing that came in its way. 



