TABLE 8

Effects of changing pH on PCs

pH was lowered by HCl and lactic acid or by increasing the percentage of CO₂. It was elevated by NaOH and NaHCO₃ or by increasing the percentage of O₂ of gas.

	n	pH
	n	6.6	6.8	7.0	7.2	7.4	7.6	7.8	8.0
HCl/NaOH	8	0	0	0	6^p	8^p	8^p	7^t
Lactic acid/ NaHCO₃	6	0	0	0	3^p	6^p	6^p	6^t
CO₂/ O₂	5	0	0	0	1^p	5^p	4^p,1^t	5^t

n is the number of rings examined. p, the number of rings with PCs; t, the number of rings with TCs.