RAINEY, ON STARCH GRANULES. / 



This, when put into cold water, affords a solution, which is 

 turned brown by the action of iodine. This is a solution of 

 dextrine. I also obtained a similar solution by mixing 

 potato starch with sulphuric, muriatic, and nitric acids. But 

 I generally employed that made with muriatic acid, in con- 

 sequence of its not precipitating the lime from the gum, 

 which sulphuric acid did, as a sulphate of lime, and hense 

 did not require purified gum to be employed in the experi- 

 ments with it. I employed, likewise, a dextrine made by 

 dissolving soluble gum in water with citric acid. This I did, 

 in consequence of the muriatic and sulphuric acids having a 

 particular action upon gum— that of converting it into a 

 transparent insoluble substance, which the citric acid does 

 not. 



To show the effect of a solution of gum in precipitating 

 starch from dextrine, the same mode of experimenting as that 

 just described in reference to its action upon the juice of 

 plants may -be employed. One way which I have found con- 

 venient to demonstrate the action of gum upon a solution of 

 dextrine, is to put on a microscope slide a few drops of very 

 thick solution of gum, and on the top of that a drop or two of 

 solution of soluble gum, or of starch, acted upon by an acid, and 

 then to examine these with the microscope whilst the action 

 is going on, and without placing upon them any cover of glass, 

 when it will be seen that the solution of gum causes the 

 solidification of the dextrine starch in minute particles, 

 having a finely granular appearance. The two solutions seem 

 also to exert a repellant action on one another, and the 

 starch runs into globular forms, just as oil would do if placed 

 on water. To show this fact, and the form given to the 

 starch, these solutions should afterwards be allowed to dry 

 on the slide, and a drop of solution of iodide of potassium, 

 containing also some tincture of iodine, added ; and then over 

 them a cover of thin glass may be placed. The form which 

 the starch had taken will be seen by the colour imparted 

 to it by the iodine. On washing these with water the circular 

 patches of starch will be broken up, but the starch itself will 

 remain solidified in granules of various shapes and sizes. 

 With a view to determine how far these effects might be 

 attributable to the medium in which the starch had been 

 dissolved, I dissolved some potato starch in a solution of 

 caustic potash, and, after having filtered the solution until it 

 was entirely without any solid matter, placed a drop of it 

 upon a solution of gum, and proceeded precisely in the same 

 manner as described in the last experiment. I found that 

 exactly the same effect was produced, that is, the solidifica- 



