34 PHOSPHORUS METHOD. [CH. II 



(48) Engehnarm's blood-method^. 



Pass a stream of CO2, or of hydrogen, through some 

 defibrinated bullock's blood = so that it may take on a dark 

 venous colour. A filament of Spirogyra about 1cm. in 

 length is mounted in a drop of the blood under a cover 

 slip. The preparation is now placed in a bright diffused 

 light, and in about 15 minutes a stripe of scarlet, due to 

 arterial blood, is seen to border the alga. In sunlight the 

 scarlet tint appears more quickly. 



According to Engelmann the most delicate method of 

 showing the evolution of the oxygen is by means of the 

 spectroscope, the spectrum of the blood changing as the 

 oxyhsemoglobin appears. 



(49) Boussingault's phosphorus method^. 



Fill a bell-jar over water with hydrogen and add a 

 small proportion of CO2, i.e. not more than 8 per cent, of 

 the volume. Introduce a stick of phosphorus and a 

 leafy branch. The oxygen in the intercellular spaces of 

 the plant will attack the phosphorus, and the bell-jar 

 will be filled with white fumes. The bell-jar must there- 

 fore be placed in the dark for two or three hours, or until 

 the white vapour is dissolved in the water, and the 

 contents of the jar are clear and transparent. The bell- 

 jar is now exposed to the sun when in a few minutes it 

 becomes clouded with white fumes. We find that, when 

 replaced in the dark, a quarter of an hour is sufiicient for 

 the absorption of the fumes. 



^ PJluger's Arehiv, Vol. xlii. 



'' According to Engelmann the blood may be elightly diluted. 



2 See Deherain, Chimie Agricole, p. 82. 



