200. The colorimetric determination of pH in milk and whey by means of the “Wulff” pH tester

It has been repeatedly pointed out(1, 2, 3) that the properties of cheese during the different stages of its manufacture should be correlated with the hydrogenion concentration rather than with the titratable acidity. Little systematic work has, however, so far been carried out in this direction, except for a study of the relationship between pH and titratable acidity in Cheddar cheese by Brown & Price(4). In planning work on similar lines, it was realized that the potentiometric methods of determining pH require expensive equipment and skilled attention, so that a supplementary colorimetric method, if sufficiently accurate to indicate the major changes in pH, should appeal more strongly to the practical cheesemaker on account of its cheapness and simplicity and the ease with which the outfit can be transported.

49. The Influence of Bacilli of the Colon Group on the Production of Acid by Lactic Streptococci in Milk

1. Colon bacilli grown in milk for from 3 to 16 hours partially inhibit the subsequent formation of acid by lactic streptococci.2. The inhibition is not entirely accounted for by the increased hydrogenion concentration nor by the lactic acid produced by the colon bacilli. Other substances which have a retarding influence on the streptococci are evidently formed in milk cultures of colon bacilli. The action of these substances is not significantly modified by heating at 75°C. for one hour.3. The possible practical significance of the phenomenon is discussed.

On the Use of Sodium Bicarbonate and Calcium in the Rectification of Sea-Water in Aquaria

The use of sodium bicarbonate for the maintenance of the proper hydrogenion concentration and bicarbonate content in marine aquaria using a closed circulation, was recommended by Breder and Howley (1). It was pointed out by them that this substance was more suitable for such purposes than quicklime which is used in the Plymouth Aquarium, because the latter “disproportionately increases the calcium content.” Atkins (2) disagrees with this opinion chiefly on the grounds that sulphates from metabolized food do not tend to increase the acidity of the water. Atkins quotes Smith (3) as stating that the urinary SO4 comes from ingested sea-water, and neglects entirely the fact that Smith had reference to the bulk of the urinary salts. As Smith remarks on page 494, a fraction of the urinary S04 is of metabolic origin, and this fraction is of course the only S04 which is significant in the problem discussed by Breder and Howley.