416 Scientific Proceedings, Royal Dublin Society. 



pH value for sea-water is about 8"2 ; it is, therefore, slightly alkaline, or, in 

 Wherry's terms, it has a specific alkalinity of over 10. 



As far as the writer is aware, but few plant-saps are alkaline, and those 

 only very slightly so, as, for example, the roots of wheat, as found by 

 Kappen (1918). Haas (1916) has drawn atteniion to the fact that the sap 

 may in some cases lie between pH 7 and 8. The writer has found some marine 

 algae to be alkaline pH 7'3 or slightly less. Colorimetric work may, where 

 clear sap solutions are available, be brought to much precision by the use of 

 a Kober (1917) colorimeter, as pointed out by Duggar and Dodge (1919). 

 The writer has found the Duboscq colorimeter very satisfactory for the purpose 

 also. All researches based on electrometric or colorimetric estimations on 

 expressed sap are open to possible sources of error in the changes undergone 

 during extraction. For example, as shown by Mason (1920), leaves exposed 

 to toluene vapour, in order to increase the permeability of the cells and to 

 render the expression of the siip easier, are found to develop a considerable 

 amount of heat owing to rajDid oxidations. The well-known browning of 

 many plant juices when expressed shows the influence of oxidation, which 

 may alter the acidity. McClendon and Sharp (1919) record a change in 

 carrot juice from pH 5'85 to 5'73 on standing twenty minutes in air. For 

 this reason the work of Haas (1916) is of special interest, inasmuch as he uses 

 the anthocyan pigments of petals as natural indicators of reaction in the 

 living cell. It has frequently been assumed that a red colour denotes an 

 acid cell-sap in the petal, and a blue an alkaline. Haas, however, extracted 

 the pigments, and observed the colour given when in solutions of known pH. 

 In this manner he showed that, for example, the pansy, which is blue, yields 

 an anthocyanin which is rose from pH 1 to pH 4, blue at pH 5, and blue- 

 green from pH 6-8. From pH 9-11 it is green, and finally yellow atpH 12. 

 It is clear, therefore, that the living cells are in the neighbourhood of 

 pH 5. It is accordingly not alkaline, but of well-marked acidity. The fading 

 of colour in the cells as, they die is accompanied by a decrease in acidity. 



Deterndnatio7is involviiig small quantities of liquid. 



When only small quantities of liquid are available it is often allowable 

 to dilute the solution sufficiently for the pH to be determined with very 

 approximate accuracy. As pointed out by Clark (1920), under certain condi- 

 tions the effect of dilution is almost negligible. This device may be employed 

 with advairtage for highly coloured or turbid solutions. 



Haas (1919) made use of the comparison of drops of solution on white 

 porcelain against drops of standard solution, with addition of a suitable 



