232 Dr Daffy's Observations on Fish, 



reaction, as denoted by test paper ; whilst in their roe and 

 milt I have detected very little saline matter, no trace of 

 iodine, or of free alkali ; on the contrary, a free acid, the 

 phosphoric, analogous to what occurs in the ash of the yolk 

 of the domestic fowl, — and in consequence of which, the 

 complete incineration of the roe of the fish and its milt, like 

 that of the yolk of the egg, is very difficult. 



The same conclusion, on the same ground, viz., the ab- 

 sence of iodine, is applicable to fresh- water fish, — a conclu- 

 sion that can hardly be tested by experience, nor is it of 

 practical importance, since fish of this kind enters so spa- 

 ringly into the ordinary diet of the people. 



Lesketh How, Ambleside, 

 April 14, 1853. 



P.S. — I have mentioned briefly the test employed to detect 

 iodine. To prevent obscurity, may I be permitted to add a 

 few particulars relative to the mode of proceeding ? On a 

 portion of starch in fine powder, that is, in its granular state, 

 aqua regia is poured, or about equal parts of nitric and mu- 

 riatic acid, in a platina capsule, and then well mixed, using 

 a glass rod. The salt to be tested, either in solution or solid, 

 is then added. The blue tint due to the presence of iodine 

 is immediately produced, if any of this substance, or a suffi- 

 ciency of it to take effect, be present. The delicacy of this 

 test is, I believe, well known. I have by means of it de- 

 tected iodine, when one-tenth of a grain of the iodide of 

 potassium was dissolved in 16,775 grains of water. Rela- 

 tive to this method, I may further remark, that by well mix- 

 ing the acid and starch, not only is the starch reduced to a 

 gelatinous state favourable for being acted on by the iodine, 

 as liberated by the action of the chlorine, but also that the 

 excess of chlorine is, to a great extent, got rid of. The 

 platina capsule has appeared preferable to one of glass, as 

 shewing the effect of colour by reflected light more readily 

 and distinctly ; and also, I am disposed to think, from some 

 peculiar influence which the metal exercises, favouring the 



