PROCEEDINGS OF THE POLYTECHNIC ASSOCIATION. 629 



the seccharometer indicates 10 per cent., will probably yield six 

 barrels of sugary liquid, which, after complete fermentation with 

 beer yeast (75 to 90 deg. Fahr.), may be poured at once upon the 

 vinegar generators, and ^^^ll yield a vinegar containing a little lesd 

 than seven per cent., by weight, of hydrated acetic acid, and fully- 

 strong enough for household purposes. 



New Formula for Silvering Paper. • 



At the November meeting of the American Photographical So- 

 ciety, the following new formula for composition of the silver 

 bath, by Henry J. Newton, of New York, was presented: water, 

 one ounce; nitrate of silver, twent^'-five grains; ujtrate of magne- 

 sium, twenty-hve grains; nitrate of potassium, twenty-five grains; 

 acetate of lead, five grains. Let the solution stand for several 

 hours in the sun; filter, then float the paper about three minutes, 

 and tone as usual. The formula was commended by practical pho- 

 tographers Avho had experimented with it. 



Prof. S. D. Tillman remarked, viewing the compound from a 

 theoretic standpoint, he should at once decide that the magnesium 

 salt was a beneficial ingredient in this mixture, and one likely to 

 lessen the amount of silver essential to the operation of preparing 

 the paper. Magnesium, although a biatouic metal, forms haloid 

 compounds, often found associated with the alkaline haloids. Mao-- 

 nesium, in the process of combustion forming magnesia, generates 

 the complete series of waves which produce white light. We 

 know the actinic waves are present from the fact that this light 

 will cause a mechanical mixture of chlorine and hydrogen (inert in 

 the dark or under the j^ellow ray) to instantaneously combine 

 chemically and form hydrochloric acid gas. The atomic weight of 

 magnesium is double that of carbon, and as a multiple of the latter 

 may be classed with silver. 



The remarkable sensitiveness of nitrate of silver, under the 

 action of light, and the almost instantaneous distraction of color 

 in certain substances with which it combines, probably results 

 from the neutralizing effect of one portion of its components upon 

 another. They have peculiar numerical relations, which may be 

 expressed in the old notation, thus : (N O^) x Ag x O, in which the 

 combining weight of the first term (54) is just one-half that of the 

 second term (108). The absence of color or the entire absorption 

 of light may result from the interference of two series of waves, 

 rendered similar by action of the compound, which is aptly illus- 



