106 BOTANICAL GAZETTE [ AUGUST 
Although phosphoric acid is a tribasic acid, the electrical 
conductivity of its solution shows that it splits up chiefly into 
the ions H* and H, Poj,** and consequently we should expect 
2t See Ostwald’s Lehrbuch, /oc. ci¢. 
a solution containing phosphoric acid (made up molecularly) to 
show the same concentration at which the plants will grow in tt 
as a solution of hydrochloric acid for instance, for the content of 
hydrogen ions is the same in both cases. Experiment verifies 
this as table 35 shows. 
35. Hyprocyanic acip (HCN). 
(Begun March 2, 4 P.M.) 
Concentration Length Length : 
gm. mol. per liter} March 3,5 Pp m. | March 4, 3 P.M. Remarks 
sto0 io dead 
vies 16.5 * “ 
rato 17,0 a 17.90mm ‘“ 
Ere 21.5 “ : alive 
25600 ohn « 
eset es 21.0. ** ‘“ 
sid00 an5 “ 
ee ee 39 5 “ee ‘“ 
36. PHospuoric acip (H,PO,). 
(Begun January 31, 4 P.m.; closed February 1, I P.M.) 
Concentratio: 
gm. mol, perliter Length Remarks 
szoo po flabby, dead 
gna 19.5 “ “ “ 
sz00 335 ~ apparently normal : 
ery 28.5 (73 ‘ec ‘“ 
rat00 27.0 ‘“ ‘“ ‘“ 
ok 21.0 “ é ‘“ o 
ee | 
Tate 36 shows the toxic effect of a solution of chromic pe ae 
This is a weak acid and is probably not completely dissociate? * a 
ous concentration at which the roots survive in it. hethet © 
ion ~Cr, O- e only 
is harmless at this concentration can of cours 
: 
