SULPHATE OF SODA, SULPHURET OF SODIUM, CARBONATE OF SODA. 191 



try perhaps in larger quantity or more extensively than in England. 

 That it has often failed to benefit the land in particular localities, only 

 shows that the soil ii. those places already contained a natural supply of 

 this compound large enough to meet the wants of the crops which grew 

 upon it. The facts above stated as to the influence of the wind in top- 

 dressing the exposed coast-line of a country with absolution of salt, may 

 serve as an important guide both in reference to the places in which it 

 may be expected to benefit the land, and to the causes of its failing to 

 do so in particular districts. 



2°. Sulphate of Soda, or Glauber's salt, is usually manufactured from 

 common salt by pouring upon it diluted sulphuric acid (oil of vitriol), 

 and applying heat. Muriatic acid (spirit of salt, so called by the old 

 chemists, because thus given off by common salt,) is given off in the 

 form of vapour, and sulphate of soda remains behind. It may also be 

 prepared, though less economically, by adding (he common soda of the 

 shops (o diluted sulphuric acid as long as any efTervescence appears. 



This well known salt is met with in variable quantity in the ashes of 

 nearly all plants, and is diflfused in minute proportion through most 

 soils. I have elsewhere [see Appendix,] directed your attention to the 

 beneficial,efrect which it has been observed to exercise on the growth 

 especially of such plants as are known to contain a considerable propor- 

 tion of sulphuric acid. Among these are red clover, vetches, peas, &c. 

 And as this salt is manufactured largely in this country and can be ob- 

 tained at the low price of ten shillings a cwt. in the dry state,* I have 

 recommended it to the practical farmer as likely to be extensively useful 

 as a manure for certain crops and on certain soils. The kind of crops 

 and soils have as yet in great measure to be determined by practical 

 trials. — [See the results of Mr. Fleming's Experiments, given in the 

 Appendix.] 



3°. Sulphuret of Sodium. — When sulphate of soda is mixed with 

 saw-dust, and heated in a furnace, the oxygen of the salt is separated, 

 and sulphuret of sodium is produced. By a similar treatment sulphate 

 of potash is converted into sulphuret of potassium. These compounds 

 consist of sulphur and metallic sodium or potassium only. They do 

 not occur extensively in nature, and are not manufactured for sale; but 

 there is reason to believe that they would materially promote the vege- 

 tation of such plants as contain much sulphur in combination with pot- 

 ash or soda. The sulphuret of sodium is present in variable quantity in 

 the refuse lime of the alkali works, already spoken of, and might be ex- 

 pected to aid the other substances of which it chiefly consists, in contri- 

 buting to the more rapid growth of pulse and clover crops. 



4°. Carbonate of Soda. — I have described the above compounds of 

 soda before mentioning this its best known and most common form, be- 

 cause they are all steps in the process by which the latter is usually pre- 

 pared from common salt, by the soda manufacturers. 



When the sulphuret of sodium is mixed with chalk in certain propor- 

 tions, and heated in a furnace, it is deprived of its sulphur, and is con- 

 verted into carbonate of soda, the common soda of the shops. 



This well known salt, now sold in the state of crystals, [containing 62 



• Not in crystals, the for^nn which it is commonly sold as a horse medicine. These- 

 crystals contain upwards of half their weight (55 per cent.) of water. 



