114 



CHEMISTRY. 



tungstic acid can be used in the reduction, so 

 that the percentage of error may easily become 

 large. 



Industrial hemistry. The manufacture of or- 

 ganic coloring-matters from coal-tar has made 

 enormous progress within recent years, but the 

 activity of chemists has been exerted to a 

 much higher degree in developing the appli- 

 cation of the direct products of tar- distillation 

 than in bettering the methods of obtaining 

 those products. Several of the coal-tar hydro- 

 carbons have found extensive practical appli- 

 cations in the manufacture of the azo colors. 

 The azo compounds, containing the group N 

 =N in combination with two aromatic nuclei, 

 are all colored, but the azo hydrocarbons them- 

 selves have no affinity for animal and vege- 

 table fibers, and hence can not be used as dyes. 

 On the other hand, such of their derivatives as 

 contain amido or hydroxyl groups are color- 

 ing matters. Some of these have long been 

 known, but, with the exception of aniline yel- 

 low and Bismarck-brown, the azo compounds 

 were not made use of until 1876. Since then, 

 a great number of new ones have been made, 

 many of which have been patented and manu- 

 factured on a large scale. The oxyazo colors 

 are made from a diazo salt and the combina- 

 tion of a phenol with an alkali metal. The 

 amidoazo colors are made on a large scale by 

 the action of nitrous acid on a free amine, or, 

 when this is not practicable, by the action of 

 a diazo salt on an amine. By means of these 

 reactions the number of azo colors which may 

 be formed from aromatic compounds contain- 

 ing amido and hydroxyl groups is almost in- 

 finite. The popularity of these colors has 

 become so great that the demand for the hy- 

 drocarbons used in making them has vastly in- 

 creased, and their price has risen considerably, 

 while attention has been given to means of 

 producing them in greater abundance and in 

 the state of purity in which they have to be 

 to secure perfect colors. 



The manufacture of soda by the ammonia 

 process has been greatly increased within a few 

 years past. Tables of the relative amounts of 

 soda manufactured in different countries by 

 the Leblanc and the ammonia processes, pre- 

 pared by Mr. Walter Weldon, show that out 

 of a total of 708,725 tons, representing the an- 

 nual products of Great Britain, France, Ger- 

 many, Austria, Belgium, and the United States, 

 163,225 tons are manufactured by the ammonia 

 process and 545,500 tons by the Leblanc pro- 

 cess. A new enterprise has been begun for the 

 working of the Leblanc process in connection 

 with the extraction of copper and iron from 

 Spanish and Portuguese pyrites, in which the 

 sulphuric acid evolved in that manufacture 

 will be made economically available. The Rio 

 Tinto Company is building factories in France 

 for the exploitation of a combined process in 

 which copper and oxide of iron will be relied 

 upon as the'products of chief importance, while 

 soda and hydrochloric acid will be made as 



by-products. Thus, at first soda was the only 

 product of the Leblanc process that had com- 

 mercial importance; then in time a demand 

 grew up for chlorine, and the hydrochloric 

 acid formed during the process became val- 

 uable ; next, soda ceased to be profitable, and 

 became a kind of by-product that continued to 

 be made because chlorine could not be made 

 without it. Now Leblanc soda, says Mr. Wel- 

 don, gives no profit at all, and chlorine none 

 to speak of ; and both have come to be regarded 

 as secondary products, to be made only inciden- 

 tally, and only because making them is essen- 

 tial to the application to certain ores of the wet 

 method of extracting copper. The difficulty ot 

 obtaining a supply of ammonia commensurate 

 with the extension of the demand, which it was 

 at one time thought would hinder the speedy 

 development of the ammonia process for mak- 

 ing soda, has been removed so completely 

 that, notwithstanding the great increase in the 

 development of the process, the price of am- 

 monia is falling. It is now obtained commer- 

 cially from coke-ov ens ; and Mr. William Fer- 

 rie has introduced with success a method for 

 collecting it from the gases of blast-furnaces 

 in which raw coal is used. From two of the 

 sixteen blast-furnaces at the Gartsherry Iron 

 Works in Scotland, ammonia and tar are now 

 regularly collected at the rate of twenty 

 pounds of ammonium sulphate per ton of coal 

 consumed. Thus it appears to be possible to 

 collect and utilize as ammonia a portion at 

 least of the nitrogen of nearly all the fuel 

 burned for industrial and domestic purposes. A 

 suggestion has been made that the soda-maker 

 shall entirely cease to use raw coal as fuel, but 

 shall convert all his coal into coke, collecting 

 for sale the oil and ammonia evolved during 

 the conversion, and himself using for heating 

 purposes the gases evolved during the coking 

 operation and the coke itself. It is believed 

 that the soda-maker might by this mode of 

 proceeding obtain his fuel virtually for noth- 

 ing. In the Leblanc process the chlorine of 

 the salt decomposed is yielded as hydrochloric 

 acid ; in the ammonia process it is yielded as a 

 somewhat dilute solution of calcium chloride. 

 This is a matter of small importance in Eng- 

 land, where hydrochloric acid is produced in 

 excess; but on the Continent, where the de- 

 mand for chlorine is greater than the supply, 

 it operates against the Leblanc process. M. 

 Solvay is accordingly about to try at his am- 

 monia-soda works in Dombasle, France, a pro- 

 cess for obtaining hydrochloric acid from cal- 

 cium chloride. Having concentrated by evap- 

 oration the mixed solution of calcium and so- 

 dium chlorides which is the residual product 

 of the ammonia process, he mixes it with clay 

 into balls, dries the balls and heats them to 

 redness in a current of steam, whereby he ob- 

 tains a mixture of the vapor of water and the 

 vapor of hydrochloric acid, which he dries by 

 passing through a very strong solution of bi- 

 chloride of calcium. 



