342 BOTANICAL GAZETTE: [OCTOBER 
for species are for the most part new to thestate. The list includes 226 species, 
and among them there is a new species of Oedogonium (O. americanum), and 
new varieties of Vaucheria geminata and Oedogonium undulatum. 
AN ALDERWERELT,” in continuing his studies of Malayan pteridophytes, 
has described 27 new species of ferns, among them a new genus (Campylo- 
gramma), 11 new species of Lycopodium, and 7 new species of Selaginella.— 
j. M. Cc. 
Direct reading potentiometers.—The electromotive force of the hydrogen 
electrode bears a logarithmic relation to the normal hydrogen-ion concentration 
H-+ of the solution. Where large numbers of determinations are concerned, 
the calculation of the reaction of the solution in terms of normal acidity be- 
comes laborious, An attempt to simplify the process was made by SORENSON, 
who introduced the Ph values.* Since the Ph value is the negative logarithm 
of the hydrogen-ion concentration, the relation existing between these numbers 
and the usual method of expressing acidity in terms of normality is not always 
clear. 
Bovie” has devised a potentiometer which reads directly in terms of 
hydrogen-ion concentration. In the original article a full discussion is given 
of the method of operating the instrument, as well as we the CoS ERCLO® of 
the dip electrode to be used in titrations. Thi the operator 
to titrate a solution to a definite hydrogen-ion concentration and thus peat 
the error due to misjudgment of the end point as found by the indicator method. 
Another advantage of the instrument is that it makes it possible to titrate two 
different acids in the same solution or to titrate successively the hydrogen ions 
of polyvalent acids or acid salts. It also makes possible the titration of such 
acids as boric acid, which give an end point on the alkaline side of the neutral 
ae of distilled water. The author gives a number of other very useful 
applications for the instrument. The apparatus is very well adapted for mak- 
ing large numbers of determinations rapidly and with an accuracy sufficient 
for ordinary purposes. 
Using logarithmic resistances instead of the logarithmic scale, BARTELL” 
has devised a similar apparatus, which avoids the sources of error in the BovIE 
apparatus and gives a greater accuracy. It is not expected that this type of 
potentiometer will replace the older forms which are adapted to reading very 
small potentials.—R. B. Harvey. 
9 Van ALDERWERELT, Capt. C. R. W. K., New or interesting Malayan ferns. 
8 and 9. Bull. Jard. Bot. Buitenzorg nos. 23 and 24. pp. 27 and 8. pls. 4. 1916 and 
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2 Bovig, W. T., A direct reading segura for measuring and recording both 
the actual and total reaction of solutions. Jour. Med. Research 33:297- 1915- 
 BarTELL, F. E., A direct a ionometer. Jour. Amer. Chem. Soc. 39:63°- 
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