AMERICAN INSTITUTE. 553 



clear, yellowish color, transparent, limpid, and tlie odor of the 

 fruit, quite agreeable taste, and its specific gravity is 0.917. 



The olive oil is adulterated with oil of poppy, sesame, and 

 arachis. 



The specific gravity of pure filtered whale oil is from 0.9155 to 

 0.9303, in thirty samples examined. 



These gravities are perfectly proved. 



[Journal of the Society of Arts, London, April 25, 1856.] 



PHOTOGALVANOGRAPHY, OR ENGRAVING BY LIGHT 

 AND LIGHTNING. 



A paper was read from Herr Paul Pretsch, late manager of the 

 Imperial Printing office, Vienna. 



"Having been for many years engaged as manager of the Impe- 

 rial Printing office, at Vienna, soon after the introduction of pho- 

 tography, I felt the importance of this beautiful art in re-prj- 

 ducingand imitating most of the wonderfid productions of nature 

 and art. I was entrusted with the power to establish photography 

 at the office, and gained a prize medal at the exhibition of 1851. 

 I entertained the idea that I could by photography obtain a plate 

 from which we might print with common printers' ink. Many 

 learned men believed in its importance and possibility. Dr. Berres 

 in Vienna, was one of the first to make important investigations. 

 He executed prints from etched daguerreotypes, of great merit. 

 He used a solution of gum arabic and nitric acid. There was 

 about that time a process which gave very perfect but feint 

 results; it consisted in the use of bichromate of potass with the 

 addition of aqua-regia, fixed by washing with ammonia. W. R. 

 Grove of London, used the daguerreotype plate as the anode in a 

 decomposing trough filled with diluted muriatic acid, and as the 

 cathode^ a platinum plate — both plates being connected with a 

 single cell galvanic battery. 



"Mr. Fizeau of Paris, etched his daguerreotype plates, by cov- 

 ering them with a mixture of nitric, muriatic and nitrous acids, or 

 with a mixture of nitric acid and nitrate of potass and chloride of 

 sodium, repeating this process several tinjes, cleaning his plate 

 each time with caustic ammonia — the faint etched lines or tints 

 were afterwards filled with printers' ink capable of drying rapidly. 

 The whole surface of the plate was then gilt, the dried ink re- 

 moved and the plate etched with nitric acid. All these investi- 

 gators have used daguerreotypes upon silvered copper, or real 

 silver plates. All of these artists were struck with the minute- 

 ness and beauty of the details, but complained of the faintness of 



