39 
temperatures, or even at 0°C., acts slowly on the oxidizable constitu- 
ents of the resin, probably extracting hydrogen and possibly carbon, 
and thereby altering the original composition of the guaiacum. 
Schoenbein ( 377 ) next turned his attention to the bluing of guaiacum 
by those substances contained in the fresh tissues of plants, and in 
1848 he gave to the chemical world the results of his first researches 
in this highly fruitful field of investigation in a communication enti- 
tled “On certain chemical reactions of the potato.” In this paper he 
refers to the observations of Planche a and Taddei on the bluing of 
guaiacum by many roots and tubers, and to the fact that the latter 
appeared to consider air as necessary for the reaction. His own 
experiments indicate that there is unevenly distributed throughout 
the potato some substance having the power of bluing guaiacum, the 
most rapid bluing being produced by the under side of the potato peel 
and at the points where the “eyes” or sprouts occur. According to 
Schoenbein, the starch and expressed juice of the potato, however, 
do not possess this power to the slightest degree, and, upon boiling, all 
parts of the potato entirely lose their power to blue guaiacum. On the 
other hand, the freshly cut peel of the potato blues guaiacum as quickly 
as does manganese dioxide or lead peroxide, and the blue solution 
shows all of the properties of that obtained by the latter method, 
fading slowly in the air at ordinary temperature, and rapidly upon 
boiling being decolorized by hydrogen sulfide and other reducing 
agents and precipitating a blue resin when added to water. He ob- 
served also that the potato, like the other substances having the power 
to blue the guaiacum resin and tincture has the power of decomposing 
potassium iodide with the liberation of iodine, the latter reacting with 
the starch of the potato to form the blue iodide of starch. For these 
reactions Schoenbein offers two alternate explanations; either that 
the potato contains a substance analogous to the peroxides, ozone, 
etc., or that it contains a substance having the power of activating the 
oxygen of the air, and thus rendering it capable of producing these 
phenomena. 
On the other hand, Nasse and Framm ( 31 °) ( see also Nassef 309 )) 
claim that fresh extracts that have been completely freed of oxygen 
by the prolonged action of hydrogen or carbon dioxide still give a blue 
; ; — : 7 ; 7 
a In all of Schoenbein’s original communications on this subject, this author 
(Planche) is referred to under the name of “Blanche.” Thus a good deal of confusion 
has been introduced into this literature, and this is met with repeatedly, even in recent 
writings on the subject. Thus this error is repeated by Nasse and Framm in an article 
entitled “Bemerkungen zur Glykolyse” (Pfliiger’s Archiv., 1896, vol. 63, p. 207), 
in which the mechanism of the guaiacum reaction is discussed; and very recently 
again by Engler and Herzog, in “Zur Erkenntnis der biologischer Oxydationsreak- 
tionen” (Hoppe-Seyler’s Zeitschrift fiir physiologische Chemie, 1909, vol. 59, p. 357). 
For the benefit of those who may be interested in the historical development of this 
subject, the writer is glad to be able to correct this error. 
■ ' . 
