Polytechnic Association Proceedixos. 957 



Magnesia is now very extensively used to prevent the oil from 

 fading. 



Dr. Vanderweyde stated that white lead is the best paint for 

 out-door work, and zinc-white for inside, as the former does not 

 fade to a yellow, if placed in the sun-light and air. He painted a 

 picture about twenty years ago; as an experiment he used white 

 lead to paint the clouds, and zinc-white for the snow on the moun- 

 tain, and the clouds are now a yellow as desired, while the snow 

 on the mountain is very white. 



Mr. J. K. Fisher said that a few hours exposure to the action of 

 the sun and shade, will make a perceptible dilference in an oil 

 canvas. Bleaching the oil is of no account, if it will return to its 

 natural color. 



In relation to the item on preserving wine, Dr. Bradley remarked 

 that sulphm-ous acid will preserve cider from becoming sour. 

 When the cider has reached the proper conditions, and it is desired 

 to keep it there, the cider is put into a clean barrel, and when about 

 two-thirds full, the fumes of sulphur are let into the barrel. The 

 sulphur seems not to affect the taste of the cider, but keeps it 

 fresh for a year. 



Dr. Vanderweyde stated that when a barrel of wine has reached 

 a certain degree of flavor, the fumes of sulphur are admitted into 

 the bottles in which the wine is to be placed, and it is thus kept, 

 but if there is an excess of sulphur, the wine will taste of it. The 

 sulphate of lime will do the same thing, but, the doctor humor- 

 ously added, many people cannot stand this in their stomachs, as 

 it is apt to form plaster of Paris. 



The Chairman remarked that sulphurous acid and the alkaline sul- 

 phites will destroy minute organisms, which produce zymotic action. 



Prof. Horsford, of Cambridge, was one of the first, if not the 

 first, to use sulphites for arresting fermentation and further change 

 iu cider. 



NEW WOOD SCREWS. 



Mr. T. D. Stetson exhibited Pratt's patent wood screw, made 

 with three threads, which admits of its being driven in to the wood 

 with a hammer. They were used on the Hai'lem road, for fasten- 

 ing the rails, with much success. 



SAFETY VALVES. 

 Mr. Charles E. Emory, of the Novelty Iron Works, placed oh 

 the blackboard g, formula with the following explanation: 



