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Here again, then, it is to uric acid, present, however, in small quantities in the adipose tissue, that the caterpillar's rich livery is due. The black parts are an exception. Unassailable by nitric acid, they retain their sombre tint after treatment as before, whereas the portions stripped of their pigment by the reagent become almost as transparent as glass.
On solution in alcohol, and digestion for two days with animal charcoal, the color was much diminished, and on the liquid being filtered and cooled to 0° C., an abundance of small white crystalline plates separated out, which, when dried, melted at 67° C. The crude fatty acids turn black with sulphuric acid, as the oil does, and yield a similar substance with nitric acid.
Many of these limestones are of such composition as to be acted on freely by the elements of the atmosphere, which, in the form of nitric acid, combine with the earthy and alkaline bases of calcareous rock, and give rise to the formation of nitrates with the liberation of carbonic acid; hence the disintegrated rubbish of the caves yields nitrate of potash after being treated with the ley of ashes and subsequent evaporation of the saline lixivium.
It does not appear to have occurred to him that Hayward's process and his own were essentially the same. A chemical dictionary would have informed him that sulphuric acid enters largely into the composition of aquafortis, from which he might have inferred that the only difference between the two methods was, that Hayward employed the sun, and Goodyear nitric acid, to give the sulphur effect.
It is their magnificent opaque white granulations which, seen through the transparent skin, form the snow-white stripes in the live Spider. Treated with nitric acid on the microscopic slide, they do not dissolve nor produce effervescence. Uric acid then is not present in this case; and the substance must be guanine, an alkaloid known to be the urinary product of the Spiders.
We should have lost the pleasure and instruction of producing them by aid of our own wits and energies. To encounter and overcome a difficulty is the most interesting of all things. Hence, though often baffled, we eventually produced perfect specimens of nitrous, nitric, and muriatic acids.
Thirty to 40 grammes of nitric acid are added to 1,000 grammes of wood-spirit, such as is generally used in photography, and the prepared pieces of glass are dipped into the bath, leaving them afterward to dry. If the bath becomes of a yellowish color, it must be renewed.
They will be as certain to use their freedom of will only in particular ways as to be driven into those ways by obedience to fixed laws. It is they that form the point of contact between this universe and something else quite different in which none of those fundamental ideas obtain without which we cannot think at all. So we say that nitrous acid is more reliable than nitric for etching.
"Because it burnishes better, and because it assists in fixing the layer of gold, rendering it less susceptible of being removed in scales when heated too much." Rotten Stone. "Purchase the best ground rotten stone of the druggist, put a few ounces at a time in a wedgewood or porcelain mortar, with plenty of clean rain water. This should have about forty drops of nitric acid to the quart.
"Well, perhaps these two tests will be sufficient. What is your excellency good enough to think on that score?" asked the supposed Valyajnikoff. "What is the need of further tests? The matter is clear enough," assented the prince. "If it is satisfactory, we shall proceed to make it even more satisfactory. Here we have a touch-stone, and here we have some nitric acid.
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