CHEMICAL SCIENCE. 205 



any future accumulation of acid, I propose to keep suspended in 

 the oil a small quantity of a substance in powder which shall neu- 

 tralize any acid which may be generated, and which of itself shall 

 have no action on the oil. This method is oflered as an efficient 

 prevention of spontaneous decomposition. The amount of neu- 

 tralizing powder required is very little, — sixty grains to the pound 

 of oil might be sufficient. The quantity is so small that it would 

 not interfere with the use of the oil, and need never be removed 

 from it. 



In actual practice, one or moi'e of these plans may be combined. 

 The fourth is compatible with all the others, and should he used 

 with all the others. Nitroglycerine should not be kept in storage 

 unless it is free from the danger of its most formidable property, 

 — the liability to spontaneous change. 



In conclusion, I can say that I have as yet had no reason to 

 modify the opinions which I expressed in my communication of 

 May 5 ; and that I still hold that the manufacture, transportation, 

 and use of nitroglycerine may be carried on with safety. 



COLOKS FROM COAL TAB. 



Aniline, or coal-tar colors have now been extended in number, 

 so that all the colors of the rainbow, and all the shades, can be 

 obtained from coal tar. Aniline was discovered by Unverdorben 

 in 1826, who procured it by the destructive distillation of indigo. 

 It is now obtained in small quantities directly from the destructive 

 distillation of coal, as in gas-works, but is genei'aliy manufactured 

 from the lighter coal-tar naphtha. When the naphtha is rectified, 

 the portion which distils over at a tenqDcrature of 180° Fahr. is 

 benzole, and this substance was discovered by Faraday in 1825. 

 By the action of strong nitric acid, the benzole is converted into 

 nitri-benzole ; itnd this latter, when agitated with water, acetic 

 acid, and iron filings, becomes aniline. By the action of oxidizing 

 agents, such as chloride of lime, bichromate of potash, chloride of 

 mercury, etc., the aniline, which is colorless by itself, can be trans- 

 formed into all shades of violet, mauve, magenta, etc. By the 

 researches of Hofmann, the number and beauty of the aniline col- 

 ors have been increased. While numberless shades of reds and 

 purples can be obtained, there is a splendid green, called ver- 

 dine, discovered by Eusebe, and which remains a true, pure green 

 even by candle or gaslight ; a blue which is as clear as opal, a good 

 yellow, and a fair black. In short, dyes of all hues can be obtained 

 from aniline, which, in its turn, is procured from the coal tar. The 

 intensity of these aniline colors may be indicated by the fact that 

 one grain of magenta in a million of water gives a good red ; one 

 grain in ten millions of water exhibits a rose pink ; one grain in 

 twenty millions communicates a blush to the water ; and one grain 

 in fifty millions tinges the water with a reddish glow. — Mining 

 Journal. , 



18 ' 



