18 



BULLETIN 1041, L'. S. DEPARTMENT OF AGEICULTUEE. 



four varieties were opened and physical tests made to determine their 

 relative phisticity. 



Not having available a suitable plastometer, the resistance of the 

 material to pressure was measured by a simple device constructed and 

 employed as follows: To the upper end of a plunger made from a 

 piece of polished brass rod half a square centimeter in cross section 

 a small weight pan of sheet tin was attached by means of a drop of 

 solder. At just 2 centimeters from the other end of the plunger, 

 which was carefully squared off perpendicularly to the axis, a file 

 mark was made. This plunger, which was held in a vertical position 

 by a glass sleeve supported in a ring stand clamp, was so arranged 

 that the test can of material could be placed under it and the end of 

 the plunger lowered to the surface of the material. 



To carry out the test the entire end of the can was removed, the 

 plunger lowered to the surface of the test material, and weights added 

 to the weight pan until the plunger penetrated the material. The 

 sum of all the weights (weight of the plunger plus the added weights) , 

 expressed in grams, required to push the plunger into the test ma- 

 terial up to the file mark in just 1 minute was taken as the factor 

 expressing the relative plasticity of the samples. Table 2 gives the 

 figures thus obtained. They represent averages of many tests made 

 upon both ends of the cans of material tested. 



Table 2.- 



-Relafive plasticity of siceet potatoes canned in the form of pie stock 

 during the various stages of handling. 





Plasticity factor (grams). 





Freshly 

 dug. 



After curing for 10 days at 8J°F, 



Variety. 



No stor- 

 age 

 period. 



Subsequent period 

 of storage at 55° 

 10 65° F. 





10 days. 



20 days. 



Big-Stem Jersey 



230 

 92 

 104 

 216 



94 

 71 

 30 

 20 



87 

 34 

 22 

 25 



85 



Southern Queen 



20 



Nancy Hall.. 



17 



Porto" Rico 



31 







From the above it will be seen that at the time of digging all four 

 varieties gave a relatively firm product. The Big-Stem Jersey and 

 Porto Rico were especially firm. The Xancy Hall was somewhat 

 softer, but still quite firm, while the Southern Queen ranked slightly 

 lower. The figures obtained at the other stages of handling are very 

 interesting. After curing, the Big-Stem Jersey lost much of its 

 firmness but was still quite resistant to penetration. During the 

 storage period there was a slight gradual decline, but this was not 



