CONTENTS. XI 



Page 



7. Influence of the seasons on the results of field experiments, . 69 



8. When experiments are to ba rejected. Value of contradictor} 1 - and of 



positive and negative results, . . . . .72 



9. Is it desirable that experiments in practical and scientific agriculture 



should be extensively made ?..... 78 



PAET II. 



EXPERIMENTS WITH SALINE SUBSTANCES, APPLIED ALONE, AND WITH 

 LIME, CLAY, AND OTHER MINERAL SUBSTANCES. 



CHAPTER V. 



PRELIMINARY CONSIDERATIONS CONNECTED WITH THE MAKING OF 

 EXPERIMENTS. 



1. General objects or aims of field experiments, ... 84 



2. Practical and theoretical purposes for which experiments with single 



substances are made, ...... 87 



3. What is a successful experiment | -, . . . .88 



4. Can mineral or saline substances, applied alone, be depended upon as 



manures for our cultivated crops, on the generality of soils 1 . 89 



5. Circumstances in which saline or mineral applications are likely to 



produce the most sensible effects, .... 90 



6. Why saline substances are not always useful in inverse proportion to 



the quantity of them contained in the soil, . . . 92 



7. General suggestions for experiments on the most profitable time of 



applying different saline and other substances when employed 

 alone, ........ 96 



8. Equivalent quantities or weights of the different saline substances 



used in comparative field experiments, .... 98 



9. Circumstances which ought to be stated in regard to all soils and 



localities selected for experiment, on publishing the results of 

 trials made upon them, . . . . .100 



CHAPTER VI. 



EXPERIMENTS WITH SULPHURIC ACID, AND WITH THE SULPHATES OF 

 POTASH, SODA, LIME, MAGNESIA, AND IRON. 



1. Proportion of sulphur contained in our usually cultivated crops, 102 



2. Results of experiments with sulphuric acid, new experiments sug- 



gested, ........ 104 



3. Composition and general properties of the sulphates of potash, soda, 



lime, magnesia, and iron, . . . . . 1 06 



