H RAINEY, ON STARCH GRANULES. 



tion of the starch. After these had been allowed to dry on 

 the glass as before directed, the starch thus precipitated was 

 transferred from the slide to a watch-glass filled with water, 

 and allowed to remain until the gum was all dissolved, and 

 then it was washed several times. In this case it does not 

 alter its form, which is that of a granular areolated film of 

 solid matter, which, from the action of iodine upon every 

 particle of it is shown with certainty to be starch. Potash 

 does not convert starch into dextrine like the mineral acid, 

 but seems to dissolve it nearly, or entirely, unchanged.* 

 The most easy way of demonstrating the effect of gum 

 upon dextrine is to mix some solution of dextrine, 

 made from soluble gum, dissolved in a solution of citric 

 acid (this acid is used only to get a stronger solution) 

 with the solution of iodine above specified, when a purple 

 brown fluid will result, then to put a few drops of it on a 

 glass slide close to a like quantity of clear solution of gum of 

 considerable density. These must be made to mix under the 

 microscope, and the effect carefully observed. The first 

 thing which will be observable will be the precipitation of 

 the starch in very minute granules, at first colourless, but 

 afterwards, and almost instantly, becoming bine or dark 

 pink. And, if the quantity of starch be considerable, the 

 blue colour will remain for several days without changing, 

 but, if only small, it will turn gradually pink, and so will 

 remain unless fresh iodine be added, when it will become of 

 a dark color. A part of the blue tint, at first produced on 

 adding the solution of gum, is the effect of the dilution of the 

 solution of the iodized dextrine, and can be produced by 

 water, but in this case there is no precipitation, and, as the 

 solution gets inspissated by the evaporation of the water, the 

 original purple-brown of the dextrine becomes restored. 

 For this experiment starch treated with muriatic acid, or, 

 sulphuric will not answer in consequence of a part of the 

 starch only being converted into dextrine, and the other 

 being held in solution, so that when the iodine is added 

 the latter is precipitated. When the solution contains only 

 dextrine nothing is thrown down by the iodine. 



The result of these experiments, taken altogether, shows 

 that so completely is gum a precipitant of starch that it 

 matters not whether it is in solution in an acid, or an alkaline 

 menstruum, the effect is the same, although in these two cases 

 the characters of the starch thus deposited are, as before 



* When potasli is employed, the lime must, be separated from the gum 

 by oxalate of ammonia, otherwise the granular film of starch will be studded 

 with particles of the globular carbonate of lime. 



