PoLTTEcnmc Association Proceedings. 905 



chemicals for dyeing. It is well known that to dye an even fast 

 and brilliant shade, the coloring matter must be held in a state of 

 perfect solution; or if insoluble in the finest possible suspension, 

 so that it may be slowly and gradually delivered to the fiber. Now 

 the presence of salt impairs the balance between the solvent and the 

 color, and causes the latter to be rapidly and irregularly deposited 

 on the surface of the goods in a dull state capable of easy removal. 

 Ground tumeric is another article often mixed with salt, which 

 imparts to it a brighter appearance in the state of powder; and the 

 action of the salt in this case is veiy similar to what has been pre- 

 viously described. 



REGULATING WATCHES. 



The new observatory at Neufchatel, in Switzerland, has rendered 

 good service to chronometer makers, by enabling them to regulate 

 their watches with more exactness. Prizes are now given to those 

 makers whose watches approach nearest to perfection. A marine 

 chronometer lately tested for two months, gave 0.164 of a second 

 as the mean variation from day to day. The improvement in 

 common watches during five years will be seen by the following 

 table of mean variations in twenty-four hours: 



In 1862 the mean variation was 1 .61 sec. 



In 1863 the mean variation was 1 .28 sec. 



In 1864 the mean variation was 1.27 sec. 



In 1865 the mean variation was 0.88 sec. 



In 1866 the mean variation was 0.74 sec. 



More than three-quarters of the chronometers observed in 1866, 

 gave a mean variation per day of less than half a second. 



CORROSION OF CAST-IRON. 



The London Journal Engineering gives Grace Calvert of Manches- 

 ter the credit of making, some time since, a series of experiments 

 which resulted in the discovery that cast-iron under certain conditions, 

 undergoes a loss of strength or cohesion without a corresponding 

 ilteration of volume or size — in other words, becomes rotten. 

 Mr. Mallet, however, commenced this investigation, and deserves a 

 higher place than Calvert in this connection. The phenomenon is 

 entirely difierent from common oxidation or rusting, which affects 

 only the surface of a piece of iron, by gradually reducing its size 

 and correspondingly reducing its strength, while the interior portion 

 remains intact. Mr. Calvert immersed cast-iron cubes, each one 

 centimeter in dimension, in acidulated water. Each cube was 



