18 BULLETIN 1367, U. S. DEPARTMENT OF AGRICULTURE 
COLORING WITH ETHYLENE 
Considerable work on the constituent of the gas from kerosene 
stoves, which is the active principle in the coloring of citrus fruits, 
has been done by Denny,’ and in one of his papers he points out that 
fruit can be colored by a number of different gases, some of which 
are present in the products of the incomplete combustion of kero- 
sene. Denny showed that lemons and oranges could be colored 
with dilute concentrations of ethylene gas, and he, together with 
his associates, worked out a practical method for the application 
of this gas in a commercial way. The process, as described by 
Chace and Denny '® is essentially as follows: Ethylene gas from a 
cylinder of the compressed ethylene, which can be obtained commer- 
cially, is released in the coloring room with the fruit in the propor- 
tion of 1 cubic foot of ethylene under normal atmospheric pressure 
to every 5,000 cubic feet of air space. The gas is released twice 
each day, and ventilating the rooms about an hour before each 
application of gas is recommended. The temperature of the room 
should be kept between 70° and 90° F.; 80° is preferable. The same 
humidity for coloring rooms as is maintained when the gas from 
oil stoves is used is advised. For oranges in Florida this should 
be about 85 per cent relative humidity. 
Denny devised a tank for use with ethylene which consists of an 
iron cylinder of convenient size capable of withstanding 500 pounds 
pressure and equipped with a pressure gauge, so that the quantity 
of the gas released into it from the cylinder can be measured. It 
is necessary to calibrate the tank by releasing some of the gas into 
it, noting the gauge pressure, and then measuring the volume of gas 
delivered from the tank at ordinary atmospheric pressures. Inas- 
much as the gas is inflammable and explosive when mixed with 
certain concentrations of air, it is important that fire should be 
kept away from the gas apparatus and out of the coloring room 
when ethylene is used. If the weather is such that it is necessary 
to heat the rooms to obtain the proper temperature for coloring, it 
should be done with steam, hot water, electric heaters without glow- 
ing wires, or some such system. In the work in Florida it was found 
possible to color with ethylene Valencia oranges showing 10 to 20 
per cent color in 72 hours, holding the room between 70° and 80° 
¥’. with a humidity of 85 per cent. These experiments were carried 
on in the spring on Valencia oranges which had become green, as 
this variety frequently does in the late spring. Oranges in this 
condition are particularly hard to color. The fact that they colored 
up readily in 72 hours, which is about the time required for this | 
variety with stove gas, indicates that ethylene may be .a practical 
substitute for gas made by a kerosene stove. 
DISCUSSION 
In a general consideration of the accumulated data on the color- 
ing of citrus fruits either by gases formed by the incomplete com- 
bustion of kerosene or by those of similar origin, it is evident that 
the process presents no particular difficulties from the operation 
7H. E. Denny. See footnote 4, p. 3. 
8H}. M. Chace and F. E. Denny. See footnote 2, p. 1. 
