Paper, 'Observations and experiments upon the foregoing preparation' by John Brown [Browne] Browne tries the method of creating Prussian blue (see CLP/11ii/2) and deduces that the volume of oil of vitriol [sulphuric acid] used in production of the dye impacts the shade of blue, as does the amount of iron in the solution. This is the second part of Browne's paper, focusing on the role of iron, published in Philosophical Transactions. The first part is found at CLP/11ii/3. Subject: Chemistry Published in Philosophical Transactions as 'Observation and experiments upon the foregoing preparation'. Read to the Royal Society on 16 April 1724. [1724]