Manganic and Hypermanganic Acids, Sfc. 183 



binoxide of manganese, yields manganate of barytes. If, 

 to a solution of the hypermanganate of barytes a solution of 

 barytes be added, and the liquid be allowed to stand a long 

 time in ajar, which it about half fills, then green crystals 

 separate themselves, which are manganate of barytes, and 

 which, like the sulphate of barytes, are insoluble in water. 



III. — Hypermanganic Acid and its Salts. 

 If manganate of potash be treated with a solution of 

 caustic potash, it dissolves without decomposition, and if 

 the solution be evaporated in vacuo we obtain again crystals 

 of manganate and hydrate of potash, which latter, under 

 the air pump, may be obtained of great beauty. If, on the 

 contrary, the manganate of potash be dissolved in water, it 

 is decomposed; a brown crystalline precipitate falls down, 

 which appears to be a combination of binoxide of manganese 

 with potash. This precipitate is decomposed when it is 

 washed, the water dissolving the potash, and converting it 

 into pure hydrated binoxide. The solution has a deep red 

 colour, and if it be evaporated till crystals appear on the 

 surface, and the solution poured off, from any precipitate 

 which may have appeared into a warmed dish, then beau- 

 tiful deep red crystals are obtained when it cools. The 

 same thing happens when a solution of manganate of potash 

 is exposed to the air so that it can attract carbonic acid ; 

 as soon as the excess of alkali is saturated the solution 

 becomes red, and at the same time a precipitate appears. 

 Hence, we sometimes obtain a mixture of these red crystals 

 during the preparation of manganate of potash, if the solu- 

 tion during evaporation be so situated that it is exposed to 

 much carbonic acid. 



fTo be continued. J 



Article IV. 



On some Methods of Astronomical Observation. By William 

 Galbraith, A.m., Teacher of Mathematics, Edinburgh. 

 {Continued from page 135.) 



Ill* — On the method of finding the value of the divisions on 

 the scales of levels applied to altitude and azimuth circles, 

 registering observations, h)C, 



