104 PROCEEDINGS OF SECTION B. 



9.— THE DESTRUCTIVE DISTILLATION OF PRICKLY PEAR, 



By F. H. Campbell, M.Sc. 



The menace of various species of the genus Opuntia popularly 

 grouped together under the name of prickly pear has become so great 

 in Southern Queensland and Northern New South Wales that it appeared 

 to the author worth while to make an investigation into the products 

 of the destructive distillation of tlje plant. From the outset it was 

 recognised that the high water-content of the plant (about 90 per cent.) 

 rendered the probability of the attainment of commercial success 

 doubtful, but since no work had previously been done on these lines 

 even an investigation unsuccessful from that pouit of view would not 

 be without vabie. It is because that opinion is still held that the author 

 ventures to present the results of his investigation. 



After a numl ler of preliminary experiments on a small scale in which 

 a hard glass retort was used, distillation was carried out in an iron 

 tube 15 inches long by 2*5 inches in diametei, closed at either end by 

 screw caps which were rendered secure by fire-clay lutes ; one of these 

 caps was provided with two brass tubes, through one of which the 

 products escaped, the other, which was about 6 inches long and closed 

 at the end, allowed of the introduction of a thermometer or a tube 

 containing a salt of known melting point. During a distillation the 

 open tube was connected to a glass X'Pi^^e, one limb of which was 

 closed by a tap and served as a draining pit, while the third was con- 

 nected to a reflux condenser, from the upper end of which a tube led 

 to a gas-holder in those cases in which the gas was collected. As it 

 was found that the nature and quantities of the various products was 

 the same when green and desiccated material was used, the great 

 saving of time rendered possible by using material previously dried at 

 100° C. caused it to be preferred. It was found that the quantities 

 of the various products and the composition of the gas depended iipon 

 the rate of heating, but that results best from every point of view were 

 obtained by starting with a cold retort and gradually raising the tem- 

 perature. The rate at which the temperature was raised was controlled 

 bv observations of the rate of gas evolution. With desiccated material 

 distillation was found to take place between 200° and 700° C. Tavo 

 species of Opuntia were examined, 0. monacantha, common but not 

 troublesome throughout Eastern Australia, and 0. inermis or 0. inermis 

 var., the so-called pest pear. The products may conveniently be dealt 

 with in the order of their volatility. 



G'rts.— The composition of the gaseous mixture was found to differ 

 according to the conditions of distillation. In Table I. are given the 

 results of analyses of three samples obtained by distillation of 0. mona- 

 cantha in the verv convenient apparatus described by Bone and 

 Wheeler (J.C.S.I., XXYII. (1908), 10-12). 



