AGRICULTURAL CHEMISTRY. 161 



of too great heat by day and cold by night, and with the watering or 

 vegetation by means of dew. It is, however, in many cases only for 

 a little space after seed-time that the soil is greatly concerned in 

 these processes. So soon as it becomes covered with vegetation the 

 character of the latter determines to a certain degree the nature of 

 the atmospheric changes. In case of many crops the soil is but par- 

 tially covered, and its peculiarities are then of direct influence on the 

 vegetation it bears. Among these qualities the following may be 

 noticed: 



1. The color of the soil. — It is usually stated that black or dark co- 

 lored soils are sooner warmed by the sun's rays than those of lighter 

 color, and remain constantly of a higher temperature so long as the 

 sun acts on them. An elevation of several degrees in the tempera- 

 ture of a light colored soil may be caused by strewing its surface 

 with peat, charcoal powder, or vegetable mould. To this influence may 

 be partly ascribed the following facts. Lampadius was able to ripen 

 melons even in the coolest summers in Friberg, Saxony, by strewing 

 a coating of coal dust an inch deep over the surface of the soil. In 

 Belgium and on the Ehine, it is found that the grape matures best 

 when the soil is covered with fragments of black clay slate. Girar- 

 din found in a series of experiments on the cultivation of potatoes, 

 that the time of their ripening varied eight to fourteen days, accord- 

 ing to the color of the soil. He found on August 25th, in a very dark 

 humus soil, twenty-six varieties ripe; in sandy soil, twenty; in clay, 

 nineteen; and in white lime soil, only sixteen. It is not difficult to 

 assign other causes that will account in part for the results here men- 

 tioned; and although it has been observed that dark soils range from 

 three to eight degrees higher in temperature than contiguous soils 

 having a lighter color, it is not to color so much as to other qualities 

 that the soil owes its peculiar temperature, as is proved by the recent 

 observations of Malaguti and Durocher. They found that the tem- 

 perature of a garden soil, just below the surface, was on the average 

 6° Fahrenheit higher than that of the air, but that this higher tem- 

 perature diminished at a greater depth. A thermometer buried four 

 inches indicated a mean temperature only 3° above that of the atmos- 

 phere. Besides the garden earth, just mentioned, which had a dark 

 gray color, and was a mixture of sand and gravel containing but little 

 clay, with about five per cent, humus, the thermometric characters 

 of the following soils were observed, viz: a grayish-white quartz 

 sand; a grayish-brown granite sand; a fine light-gray clay (pipe clay;) 

 a yellow sandy clay; and, finally, four lime soils of different physical 

 qualities. 



It was found that when the exposure was alike, the dark-gray 

 granite sand became the warmest, and next to this the grayish-white 

 quartz sand. The latter, notwithstanding its lighter color, often ac- 

 quired a higher temperature when at a depth of four inches than the 

 former, a fact to be ascribed to its better conducting power. The 

 black soils never became so warm as the two just mentioned, demon- 

 strating that color does not influence the absorption of heat so much 

 as other qualities. After the black soils, the others came in the fol- 

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