Progress of Invention. 473 



Figs. 4 and 5 represent the features of land, water, snow- 

 caps, etc., which have been seen by Dawes, De la Rue, Lockyer, 

 Phillips, and others of our best observers on the southern and 

 northern hemispheres of Mars, respectively. It need hardly be 

 said that Mars never presents either pole directly towards the 

 earth : nor, if he did, would he appear as in Figs. 4 and 5. 

 These must be looked upon as maps, and they are intended to 

 enable the student to fill in tracings or copies of Fig. 3 

 with suitable details — the upper half (or rather the part above 

 the equator) from Fig. 4, the other part from Fig. 5 ; the 

 bounding circles in Figs. 4 and 5 representing the Martial 

 equator. When this is carefully done, the student will re- 

 cognize the well-known features given in works on popular 

 astronomy ; and the observer, having made several such maps 

 corresponding to different estages of rotation, will be able to 

 interpret or correct the results of his own telescopic observa- 

 tions of the planet during the first three months of 1867. 



PROGRESS OF INVENTION. 



Economic Production of Aniline. — The importance of aniline 

 and its derivatives, in a commercial point of view, has become' so 

 great, that any improvement which tends to facilitate its production 

 is of great value. It is obtained, as our readers are aware, by 

 means of benzine, which hitherto has been procured only by a some- 

 what complicated process. M. Bobcef has been able greatly to sim- 

 plify this. He dissolves the heavy oils contained in coal-tar with 

 soda, at ordinary temperatures. They are thus separated from the 

 benzine, which floats on the surface, and may be obtained quite 

 pure by mere decantation and rectification. The residue, after 

 decantation, is a product of some value. It is a combination of 

 coal tar and alkali, which constitutes a kind of soap, and has been 

 termed by M. Bobcef phenate of soda. He considers that it pos- 

 sesses all the useful properties of phenic acid. 



Delicate Test foe, Acids. — Hitherto blue litmus paper has 

 been the most sensitive test possessed by the chemists for the pre- 

 sence of an acid. Unfortunately, however, it has been found that 

 its not being reddened by a given fluid affords no absolute certainty 

 of the absence of acids. It is even inferior in delicacy to the red- 

 dened litmus paper used as a test for alkalies. M. Sclionbein has, 

 however, furnished us with a test for acids of remarkable sensitive- 

 ness. It indicates the presence of the very smallest amount of an 

 acid, being so delicate that it shows the presence of carbonic acid 

 in distilled w r ater that has been merely breathed upon. It is 

 obtained in treating cyanine blue with soda ; dissolving one part 

 of the product in one hundred parts alcohol, and adding twice its 

 volume of water to the solution. The cyanine blue is formed by 



