Nov. i, 1920 Effect of Drying Disinfected Seed Wheat 221 



the solution ( ^— - — = 18.07 ) and 49.92 per cent of the weight of the 



V50X 1.090 '/ r 



formaldehyde present ( — , ' r = 49.92 Y A 20-cc. volume 



of undiluted formaldehyde solution gave 16.1 per cent paraformaldehyde 

 by weight of the solution and 44.6 per cent by weight of formaldehyde 

 originally present in it. A 10-cc. volume, evaporated under the same 

 conditions as the other two, gave only 7.8 per cent by weight of the 

 solution and 21.5 per cent by weight of formaldehyde. From this and 

 other data we know that the quantity of paraformaldehyde appearing 

 as residue upon the evaporation of a formaldehyde solution depends on 

 the original volume evaporated. Rate of evaporation is probably the 

 determining factor, the extent of the evaporating surface being small in 

 proportion to the volume as the latter is increased. 



It has been shown (10, 14) that dilute formaldehyde solutions grow 

 stronger as evaporation proceeds. Notwithstanding this fact, published 

 statements to the contrary occur in literature relating to the use of 

 formaldehyde as a fungicide. The weakest solution analyzed by the writer 

 was a o. 113 per cent dilution. It was found by quantitative analyses 1 

 of solutions before and after evaporation that the amount of formalde- 

 hyde per cubic centimeter of solution steadily increased as evaporation 

 proceeded. Some was lost with the water, as, otherwise, the amount in 

 the last 5 cc. would have been considerably larger than it was. The 

 increased concentration was great enough to indicate a deposit of para- 

 formaldehyde upon complete drying. As shown by the following test, 

 this proved to be the case. A 0.1 per cent solution of formaldehyde was 

 made with distilled water, and 50 cc. were put in each of two 8-cm. 

 evaporating dishes and evaporated by leaving them exposed to the air of 

 the laboratory, together with two controls containing 50 cc. each of 

 distilled water. As soon as the dishes were absolutely dry (in 12 days) 

 each dish was rinsed with 5 cc. of hot distilled water, and the washings 

 were poured into test tubes. To each was added 1 cc. of Tollen's reagent. 

 Results were distinct and decisive, a dark brown color appearing in the 



1 The mosc accurate and convenient method found for determining quantitatively the amount of formal- 

 dehyde in a solution is that of Romijn (13). To 5 cc. of the formaldehyde solution are added 5 cc. N/io 

 iodin solution and so much strong sodium hydroxid solution, drop by drop, that the liquid assumes a light 

 yellow color. After a period of 10 minutes the solution is acidified with hydrochloric acid and the free 

 iodin is titrated back with Njio sodium thiosulphate solution. Every cubic centimeter of the iodin which 

 has been used up in the reaction with formaldehyde (the difference between the original 5 cc. added and the 

 amount left to react with the sodium thiosulphate) represents 0.001501 gtn. of formaldehyde present In 

 the solution. 



The analyses, repeated several times with approximately the same results, were obtained by evaporating 

 100 cc. of a 0.1 per cent solution at room temperature in an 8-cm. evaporating dish. The quantity of solu- 

 tion used, atmospheric humidity, and other factors determine the degree of concentration of the evaporat- 

 ing solution at any point in the process. In the first analysis the amount of formaldehyde per cubic centi- 

 meter of solution increased from 0.0055 S m - to 0.0069 gm. after the solution had evaporated from an original 

 volume of ioocc.to6cc. (in8 days). Inasecond analysis the increase was from 0.0058 gm. to 0.0069 gm. per 

 cubic centimeter, the evaporating solution decreasing in volume from 100 cc. to 10 cc. in an equal length of 

 time. 



