Intelligence and Miscellaneous Articles. 393 



MANGANESIC ACID AND MANGANESATE OF POTASH. 



M. Unverdorben finds that when manganesate of potash is distilled 

 with a little anhydrous sulphuric acid, that manganesic acid is evolved 

 in the form of a red transparent gas, which dissolves in water, form- 

 ing a red solution. The gas frequentl/ decomposes spontaneously 

 in the retort, v»'ith explosion, producing oxide of manganese and 

 oxygen. 



Manganesate of potash was analysed by distilling it with excess of 

 sulphuric acid, collecting the oxygen disengaged, and estimating the 

 proportion of protoxide of manganese and salts of potash remaining 

 in the retort. According to these experiments the acid consists of 



Manganese 58"74 



Oxygen 41-26 



iOO 



And the manganesate of potash, of 



Potash 25-63 



Manganesic acid 52-44 



Water 21-93 



00-00 



Ann. des Mines, 1827, p. 145. 

 The composition of a manganesic acid as above stated, differs very 

 materially from that assigned by Dr. Thomson in his "Attempt, &c.'' 

 It is there mentioned as consisting of 



1 atom of manganese 28 or 46*66 



4 atoms of oxygen 32 or 53*33 



60 99-99 Edit. 



INDELIBLE WRITING-INK. 



The following, recommended as a process for preparing indelible 

 writing-ink, or at least as a sort of a])proximation to it, — is copied from 

 the last Number of the Royal Institution Journal : " Let a saturated so- 

 lution of indigo and madder in boiling water be made in such pro- 

 portion as to give a purple tint ; add to it from one-sixth to one- 

 eighth of its weight of sulphuric acid, according to the thickness and 

 strength of the paper to be used : this makes an ink which flows 

 pretty freely from the pen, and when writing which has been executed 

 with it, is ex-posed to a considerable but gradual heat from the fire, it 

 becomes completely black, the letters being burnt in and charred 

 by the action of the sulphuric acid. If the acid has not been used in 

 sujjicient (juanttty to destroy the texture of the paper, and reduce it to 

 the state of Under, the colour may be discharged by the oxymuriatic and 

 oxalic acids and their compounds, though not without great difficulty. 

 Wlicn the full proportion of acid has been employed, a little crum- 

 pling and rubbing of the paper reduces the carbonaceous matter of the 

 letters to [)owder; but by i)utting a black ground behind them they 

 may be preserved, and thus a species of indelible writing-ink is pro- 

 cured, (for the letters are, in a manner, stamped out of the paper,) 

 which miglit be useful for some pur])oses, perhaps for the signature of 

 bank notes." 



Nrjo Scries.Yol 2. No. 11. Nov. 1827. 3E uracine,— 



