CACTUS SOLUTION AS AN ADHESIVE. 15 



SODIUM BENZOATE. 



Sodium benzoate was used in a limited way as a preservative for 

 the cactus solution. On March 14 one-fourth of a pound was dis- 

 solved ill a small quantity of alcohol and added to a barrel contain- 

 ing -10 gallons of water in which 50 pounds of cactus had been placed 

 March 13, after removing the solid portion of the pear. The mixture 

 was stirred vigorously for five minutes and later covered. On April 

 2 an examination was made and the liquid used as a spray with zinc 

 arsenite.* Only slight fermentation had taken place, and no diffi- 

 culty was encountered in applying the spray. 



The first disadvantage in using sodium benzoate for such a purpose 

 is its cost. It is somewhat more expensive than other chemicals 

 of this class, and the element of cost is a primary consideration. 

 Another feature is that it is not easily dissolved, and unless it is 

 thoroughly dissolved its powers as a preservative are considerably 

 lessened. 



On April 2 sodium benzoate was again used in the proportion of 

 1 pound to 200 pounds of cactus in 100 gallons of water. This was 

 quite a concentrated mixture, but it kept in perfect condition for two 

 weeks, at the end of which time it was used up. The average temper- 

 ature a part of the time was 80° F. 



THE COMMON PRICKLY PEAR CACTI AND THEIR CHEMICAL 



COMPOSITION. 



The common cactus or prickly pear of southern Texas is a variety 

 known as " nopal " or " nopal azul " (Platopuntia Jindheimeri 

 Engelm.). This is the variety with flat, rounded leaves and growing 

 about 4 or 5 feet high, and it is found well distributed over southern 

 Texas. It is a native species which varies considerably in coloration 

 of spines as well as in its general habit of growth. The fruit is 

 purplish throughout, more so than the more spiny variet}^ Plato- 

 puntia engelmannii Salm., which is very similar in habit of growth, 

 but usually occurs farther west than the region occupied by this 

 species. The large spineless cactus frequently cultivated, but ordi- 

 narily not occurring abundantly in the cactus plains of southern 

 Texas, is a species which has been called Platopuntia tuna Will. 

 It grows much taller than the common " nopal " and is known in 

 California as " mission pear " and in Texas as " Nopal de castilla." 

 It frequently grows 10 to 15 feet in height, with the trunk 12 inches 

 in diameter, and the joints in shape are more elliptical than rounded. 

 The fruit is considerably larger than that of the common "nooal" 

 and greenish throughout. 



