412 Dr. Thomas Thomson on the 



tual labours, let us shew him that great discoveries may 

 produce some peace and happiness ; let us cut out from the 

 history of science such leaves as tarnish her lustre ; let us 

 endeavour to persuade ourselves that in the dungeons of 

 the Inquisition a friendly voice communicated to Galileo 

 some of those consoling expressions which posterity re- 

 served for his memory ; that the thick walls of the Bastille 

 cannot prevent public opinion from apprising Freret that 

 some day the work which he wrote in prison will be one of 

 the titles of his fame; that before dying in the hospital, 

 Borelli found sometimes, in the city of Rome, a shelter 

 from the inclemency of the air, a little straw to recline 

 his head upon; that, lastly, Kepler — the great Kepler — 

 never experienced the pangs of hunger. 



Article II. 



Method of determining the Value of Black Oxide of Manga- 

 nese for manufacturing Purposes. By Thomas Thomson, 

 M.D., F.R.S., L. and E. Regius Professor of Chemistry 

 in the University of Glasgow. 



The manganese to be tested must be reduced to a fine pow- 

 der, or brought into the state in which it is used by the 

 manufacturers of bleaching-powder. To determine its 

 value, proceed in the following manner : 



Into a balanced Florence flask put 600 grains of water, 

 and 75 grains of crystals of oxalic acid. Then add 50 grains 

 of the manganese to be tested ; and, as quickly as possible, 

 pour into the flask from 150 to 200 grains of concentrated 

 sulphuric acid. This is best done by having a given weight 

 of sulphuric acid, say 210 grains, previously weighed out 

 in a glass measure, counterpoised on one of the scales of a 

 balance. You pour into the flask as much of the sulphuric 

 acid as you can conveniently. Then, putting the measure 

 again into the scale, you determine exactly how much has 

 been put in. 



A lively effervescence takes place, and carbonic acid gas 

 is disengaged in abundance. Cover the mouth of the flask 

 with paper, and leave it for 24 hours ; then weigh it again. 



