492 TRANSACTIONS OF THE 



sequently only three-eiglitlis of an inch. But, in the case of water in the 

 atmosphere, he could not see exactly hovr the changes of barometric pres- 

 sure could aflFect the heat at T?hich that state was assumed, since the pres- 

 sure acted equally in all directions, and wox;ld, consequently, press the 

 water from contact with the capsule as well as to contact; so that it really 

 did not affect the position of the globule, 



Mr. Garvey stated that the idea of barometric pressure affecting the 

 temperature did not rest upon the supposition that the water was brought 

 nearer to the heated surface by its action, but that liquids assume the form 

 of vapor when charged with sufficient heat to give them the elastic force 

 necessary to overcome the pressure under which they happen to be. Water, 

 for instance, boils at various temperatures, according to the pressure under 

 which it is ; and it is well known that, in high mountain regions, meat 

 cannot be cooked by boiling, for the water will not be hot enough ; it will 

 go into steam at a much lower temperature than at the level of the sea, 

 owing to less barometric pressure. If Prof. Lowe undertakes to cook meat 

 in an open vessel, by boiling, he will have to eat it parboiled, as he cannot, 

 in his transatlantic trip, get heat enough into water to completely cook 

 his food, by boiling, in the upper regions of the atmosphere. 



After some further discussion of the nature of the phenomenon presented 

 by Mr. Johnson's experiment, the regular subject of the evening was called 

 up, and the following paper was read, on 



PAINT AS A PBOTECTOR. 



By Charles A. Seeley, Esq., Chemist. — Paint, in the view of uiility, is 

 employed as "a protective covering to a body, against the injurious influ- 

 ences of the air, water and other destructive agencies. Wood and the 

 common metals are especially attacked by oxygen ; exposed to the air, they 

 are consumed as in a fire. Paint is the fortress which keeps out the 

 destroyer. The utility of paint is so apparent, that any study of its compo- 

 sition and properties, which will tend to improve it in any degree, is of 

 great importance. 



Paint is understood to be a mixture of a liquid and a solid, in powder. 

 The desirable physical conditions of these are : that the liquid should have 

 a certain amount of viscidity, in order to maintain the powder in suspension, 

 and that the powder should be as fine as possible, and nearly of the same spe- 

 cific gravity of the liquid. But the chemical properties are of still greater 

 importance. The liquid and solid must be such as will not injuriously 

 react on each other, and such as are not destroyed by contact with air and 

 water. The liquid should be one which by oxydation or otherwise becomes 

 a touch and somewhat elastic hard substance. Also, there should exist 

 between the liquid and solid a certain degree and kind of affinity which 

 may favor the homogeneity of the mass. The main virtue of paint resides 

 in the liquid ; the solid serves unfavorably to dilute that virtue, and favor- 

 ably by securing that kind of consistency which permits easy manipulation 



