COMPARISON OF DIFFERENT KINDS OF ALUM. Q^S 



as an ihtelliij^ent friend of mine, an excellent practical far- pingeomparcd 



n ■ .• X !• 11 -.1 1 ^ c c ^ with occasioi.- 



mer, observes, a lair estnuate ot all the advantages ot i»i- ai fallowing. 



lowing is seldom taken into the comparative calculation. 

 That land may be broui^ht to bear a crop of some sort or 

 other every year, there can be no dotibt; though it is obvi- 

 ous, that precisely the same manaj^ement cannot suit every 

 •pecies of soil. But when we compute the true value of this 

 practice, we should not reckon from the produce of a few 

 years at first, which wTll probably be higher than the average 

 at the long- run : at the same time we must consider, where 

 a proper rotation of fallows is observed, the saving of seed, 

 of labour in sowing, cutting, inning, threshing, and carrying 

 to market; and the advantage of having the land clean, and 

 reduced to a proper tilth by repeatedly plowing and stirring 

 the soil at times when the cattle and servants of the farm are 

 not required for more necessary labour. Thus when we take 

 into account the certain additional expense on the one hand, 

 to be deducted from the produce of two moderate or perhaps 

 indifferent crops; and on the other the savings in one year, 

 and the produce of a good crop in the next, beside the cer- 

 tainty of keeping the land in heart; we may perhaps be 

 inclined at least to doubt on which side the balance prepon- 

 derates, in cases where the too sanguine speak decidedly 

 without hesitation. At present it may be presumed no 

 country in Europe can be put in competition with our own 

 for agricultural skill; certainly France cannnot : as however 

 it stands foremost among the useful arts, whatever seems 

 likely to suggest any hint toward its promotion is not unde- 

 serving of notice, from whatever quarter it may come. 



VI 11. 



A Memoir on Roman Alum, compared ivith different Kinds 

 manufactured in France ; bi/ 3Iessrs, Then ard and Ro ard. 

 Abridged by Mr. Bouilhn'^Lagrange*. 



Jl HE art of manOfacturing alum ori<rinated in the East, „« * r 



^ ^ r> ' History of 



and remained for a number of years the exclusive property alum works, 

 * Annales de Chimie, vol. LIX, p. 58. July, 1806. 



T 2 ' of 



