404 



Scientific Intelligence. 



This observation suggested to the author that formic acid might be pro- 

 duced easily and abundantly by making carbonic oxyd unite with water 

 at the instant of its formation. As oxalic acid is decomposed by heating 

 into carbonic acid, carbonic oxyd and water, it occurred to Berthelot that 

 by heating this acid with some substance which should act by contact, 

 the water and carbonic oxyd would unite to produce formic acid. Glyc- 

 erin was found to answer the purpose perfectly. The author introduces 

 into a retort of 2 litres capacity, 1 kilogram of syrupy glycerin, 1 kilo- 

 gram of commercial oxalic acid, and 100-200 grammes of water. A 

 receiver is to be attached and the retort heated gently to 100° C. : car- 

 bonic acid is given off, and after from twelve to fifteen hours all the oxalic 

 acid is decomposed, while a little weak formic acid has passed over. Half 

 a liter of water is to be added to the matter in the retort and the whole 

 distilled, water being added from time to time to make up the loss, until 

 6-7 liters of fluid have distilled over. The distillate then contains almost 

 the whole of the formic acid, while pure glycerin remains in the retort, 

 and may be used again and again. From 3 kilograms of oxalic acid the 

 author obtained 1*051 kilograms of formic acid, which is very nearly the 

 theoretical amount. In this very simple and easy process it is only neces- 

 sary to proceed slowly and not at too high a temperature, since when the 

 mass reaches 190°-200° pure carbonic oxyd is given off. By this pro- 

 cess carbonic oxyd may be prepared in a state of purity, the carbonic 

 acid being first given off. The formic acid is pure and free from oxalic 

 acid. — Comptes JZendus, xli, 955 and xlii, 447. 



[Note. — Berthelot's process for preparing formic acid is so easy and 

 elegant that this important substance can hereafter be furnished at a low 

 price and in a state of purity. Its numerous and valuable applications 

 in analytical chemistry will probably be speedily recognized ; but it would 

 be well worth while to examine its action in the place of acetic acid in 

 photographic processes. — w. g.] 



6. On the determination of chlorine by titrition. — With the view of 

 rendering the end of the reaction more distinctly visible, Mohr has sug- 

 gested the addition of a little neutral chromate of potash to the liquid 

 containing the chlorid. The red color of the chromate of silver makes 

 its appearance as soon as the last trace of chlorine is precipitated as chlo- 

 rid of silver, and the end of the process is thus very distinct. Levol sug- 

 gested the employment of phosphate of soda with the same object in 

 view, but a much larger quantity of nitrate of silver solution must be 

 added in this case to produce the yellow color, and the end of the reaction 

 is therefore much less definite. In a second paper, Mohr has extended 

 the method to the determination of many other substances by first con- 

 verting them into chlorids and then determining the chlorine as above. 

 [The method appears to give in many cases satisfactory results, but it is 

 unfortunately inapplicable in the case of colored solutions. It is to be 

 regretted that the ingenious author does not give a greater number of 

 numerical data to prove the accuracy of the method in the various cases 

 to which he applies it. We would also suggest that the practice of com- 

 paring the results obtained by a particular analytical method with theory 

 by the difference should be abandoned, and that in all cases the percent- 

 age obtained should be stated. — w. g.] — Ann. der Chemie und Pharmacie, 

 xcvii, 335, xcix, 197. 



