312 Progress of Invention. 



tion than liot ; and it varies in size from that of a grain of sand to 

 several inches. It deodorizes the sewage by absorbing the offensive 



gases ; bnt when broken emits a very disagreeable odonr. A 



Harmless Green for Paperhangings, etc. — The dangerous conse- 

 quences attending the use in paperhangings of a green colour 

 obtained by means of arsenic, are well known ; an excellent sub- 

 stitute for this poisonous substance has been discovered in a com- 

 pound consisting of three equivalents of barytes and two of man- 

 ganic acid. It may be prepared by thoroughly mixing three or 

 four parts moistened caustic barytes, two parts nitrate of 

 barytes, and two parts oxide of manganese : fusing the mixture 

 in a crucible heated to dull redness : pulverizing the residual 

 mass, and washing the powder first with boiling and then with 

 cold water, in an atmosphere free from carbonic acid. In this 

 way is obtained a fine emerald green powder, which, under the 

 microscope, is seen to consist of small transparent hexagonal 

 crystals. It is applied to paper by means of thin glue, or the 



white of an egg. Zinnalin. — This beautiful yellow dye is the 



final result of the action of nitric acid on aniline or any of the dyes 

 obtained from it. Its reactions are precisely opposite to those of 

 aniline, since it is reddened by alkalies, and changed again to 

 yellow by acids. It may be obtained by adding nitric acid to 

 aniline ; a violent reaction takes place, the temperature rises con- 

 siderably, and a dense yellow vapour, having a very disagreeable 

 odour, is given off. Unless the temperature is kept within certain 

 bounds, instead of the dye being formed, the aniline will be entirely 

 decomposed. The residual liquor, which has a reddish yellow 

 tinge, is to be evaporated in a water bath ; and thus a red mass is 

 obtained. When this is pulverized, it greatly resembles cinnabar 

 (in German zinnober), and on this account, and from its having 

 been derived from aniline, it has been called zinnalin. It im- 

 parts to wool or silk a beautiful reddish colour, which is not 

 altered by light or air. It is soluble in alcohol, and still more 



readily in ether. New Method of Hardening Cast Iron. — Having 



been raised to a low red heat, it is to be plunged into a liquid 

 containing, for every gallon of water, about two and a quarter 

 pounds of sulphuric acid, and two and a quarter ounces of nitric 

 acid, and kept immersed until it is quite cold. Its surface will then 

 be found, to the depth of more than the one-hundredth of an inch, 

 as hard as tempered steel ; and no distortion will have taken place, 

 if it has been plunged as speedily and uniformly as possible into the 



fluid. Screw Float for Paddle Wheels. — It is well known that a 



great vibration is produced when the floats of the ordinary paddle 

 wheel enter and leave the water, and that they cause a large and 

 useless expenditure of power, in giving motion to a very consider- 

 able body of water. Dr. Croft has invented a float which is in 

 the form of a screw surface, and which, both by experiments with 

 models, and by calculation, has been proved free from these 

 objectionable properties. It remains, however, as yet to be shewn 

 practically that it will take a sufficient hold of the water, and will 

 economise power. Way wiser for Cabs, etc. — Everywhere there 



