GLAUBERS SALT— PHOSPHORIC ACID. 667 



the dose should not be half so strong. Its general effects are not to 

 force plants and give them a dark colour, Kke ammonia, but to con- 

 solidate their tissues, and to render them crisp as well as succulent. 

 There is no sufficient proof of its preventing mildew, as has been often 

 asserted ; nor, on the other hand, is there any satisfactory disproof of 

 that statement. 



Glaubers salt {sulphate of soda) has been occasionally recommended, 

 but it seems to have little value, and is hardly known in gardening. 

 It may produce such good effect as belongs to it as much by its sulphur 

 as its soda. According to Prof. Johnston it acts energetically on 

 Potatoes, Rye, Peas, and Beans, " not upon the straw but upon their 

 pods, increasing their number and enlarging their size." Dose, not 

 less than 1 cwt. of the dry salt per acre, applied dissolved in water, or 

 broadcast in wet weather. 



Phosphoric Acid. — It has been long known that bones exercise 

 a very powerful effect upon plants. If broken bones are used 

 as the drainage of pots, roots soon find their way down to 

 them and pierce them. Bone-dust has been used for years as 

 a most valuable manure for Turnips when drilled in with the 

 seed. The pastures of Cheshire, exhausted by the continual 

 removal of grass by the animals that grazed upon them, 

 recover their fertility when dressed with bones. To what is 

 this owing ? It was at first thought that it was the animal 

 matter contained in them which gave the value. But boiled 

 bones, and bones burnt to an ash, proved to be as ef&cacious 

 as fresh bones. Then it was imagined that the lime contained 

 in bones produced the effect ; but lime used separately had no 

 effect. Hence it became an irresistible conclusion that it was 

 the phosphoric acid that in combination with lime (pfeosp/iate 

 of lime) constitutes bones, which principally caused such un- 

 accountable fertility. Hence arose the manufacture of super- 

 phosphate of lime, by Mr. Lawes, now so Ludispensable to 

 cultivators. By mixing bones with sulphuric acid, their lime 

 is in part seized upon by the acid, and converted into gypsum 

 or sulphate of lime, and in part remains combined with the 

 phosphoric acid, forming a superphosphate (or biphosphate) 

 which readily dissolves in water, and is thus immediately pre- 

 sented to plants in a form in which it can be absorbed. Mere 

 bones, on the contrary, part with their phosphoric acid slowly. 

 The practical consequence is that mere bones continue to 



