Polytechnic Association Proceedings. fjYO 



headache. It should, however, be used with great caution. Nitrous 

 oxide {genat) is much less objectionable as an ansesthetic. 



OZONOMETRY. 



A. Cossa, in endeavoring to discover an exact method for mea- 

 suring the quantity of ozone in common air, has established the 

 following facts: 



1. A solution of pure hydrate of potassium, containing no traces 

 of organic matter, absorbs nitro-oxygen compounds without destroy- 

 ing ozone. 



2. The quantity of iodine liberated in a solution of pure iodide 

 of potassium, is in exact proportion to the amount of ozone passed 

 through the liquid, whieh may be accurately determined by means 

 of Bunsen's volumetric method. 



NEW ACTOMITER. 



Dr. H. Vogel, of Berlin, describes, in The Philadel;phia Photo- 

 grapher, his actomiter, which he affii'ms will reduce the main 

 difficulty of carbon printing to child's play. The negative is placed 

 in the light simultaneously with the instrument, which is graduated 

 like a thermometer, and left there until the instrument indicates a 

 certain degree; this degree of printing has to be previously estab- 

 lished by experiment. A strip of carbon paper is placed under 

 the negative and exposed, and gradually, as the instrument indicates 

 four, six or eight degrees, covered up. The strip is afterward 

 developed, and it is easy to see which degree of the actomiter cor- 

 responds with the best development. When the necessary degree 

 of several negatives has once been ascertained, it becomes an easy 

 matter to judge, by comparison, the requisite time for a new negative. 



NEW USE FOR ALLSOP'S ALE. 



The Bntish Journal of Photography says, those who are endeav- 

 oring to make improvements in what is technically known as the 

 '* dry process," are now turning their attention to the use of malt. 

 Cotman has made good pictures by immersing his sensitized plates 

 for two minutes in water, afterward flooding it with Allsop's table 

 beer, then draining and drying spontaneously. To develop the 

 picture, wash the plate and then cover it with a pyrogalic solution — 

 six grains to the ounce of water — pour ofl", add two drops of a 

 thirty-grain solution of silver with ten grains of citric acid to the 

 ounce. When thoroughly out, wash and intensify carefully with 

 more silver. 



