A text-book of the science and art of bread-making : including the chemistry and analytic and practical testing of wheat, flour, and other materials employed in baking / by William Jago.

  • William Jago
Date:
1895
Catalogue details

Licence: Public Domain Mark

Credit: A text-book of the science and art of bread-making : including the chemistry and analytic and practical testing of wheat, flour, and other materials employed in baking / by William Jago. Source: Wellcome Collection.

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    heat is erohaal diiriii tlie act of union. Tn eon.seciiu'nco of this ailinity for M-ater, suljihnnc acid is lara:('ly nsc'd as a desiccatini' o?- dryino- ayjent ; on exposure to tlie air tlie acid spe(>dily increases in weiylit l)y ahsorjition of water va]>our, and the air hecoines dry ; lienee, if a vessel of sulphuric acid he placed under a hell jar, it speedily produces a dry atmosphere inside. Less concentrated varieties of the* acid form .staple articles of commerce. Owing to this attraction for water, sulphuric acid is a most corrosive hody ; wood, paper, and most vegetable and animal suhstances are vigorously attacked hy it; the acid comliines with the hydrogen and oxygen of the suhstance in the proportions in which they form water, and leaves hehind a mass of carhon, together with any excess of either hydrogen or oxygen that may have heen present. This, of course, does not in all cases represent the whole of the chemical action that may have occurred. Dilute sulphuric acid contains water in excess, and thi'refore does not exhihit this dehydrating tenrUmey when jilaced in contact with other bodies ; it is well to rememh<>r this, because in a number of reactions, where dilute sulphuric acid is em¬ ployed, it ]iroduces not merely less energetic action, but action absolutely opposite in character to that of the concentrated acifl. The dilute acicl, if allowed to evaporate in contact with })aper, tire., acts in a similar manner to the strong acid, as the water dries t)ff. Hulphuric acid forms a normal and an acid series of salts, of which Na^SO^, sodium sulphate, and NallSOj, acid sodium sulphate, are, respectively, examples. IMost of the .sulphates are more or less soluble in water; calcium sulphate is only slightly so ; barium sulphate is insoluble in water and dilute acids. 8ul]>huric acid and the sulphates may be detected in solution by the .addition of hydrochloric .acid and barium chloride, when they produce a white precipitate of BaSO^. 75. Bromine, Br.j; Iodine, L; and Fluorine, F..—The.se three elements are very closely allied in jtroperties to chlorine ; they have no very intimate connection with the chemistry of wheat and tloui’. Bromine is a litpiid ; iodine, at ordinary temperaturt's, is a solid bod}'. Iodine is slightly soluble in water, readily soluble in alcohol or a solu- tioTi of potassium iodichu KT. Iodine, or its solution, produc(*s a char¬ acteristic blue colour with starch : this n'action is of great delicacy, and is an exceedingly valuable test both for starch .and iodim*. Fluoi-ine forms an acid with hydrogen, hydrolluoric acid, I IF, which is chai'.ac- terised by its power of attacking and dissolving glass, and the silicates generally. 76. Silicon, Si; Silica, SiO.^; and the Silicates.- Silicon is .an element somewhat re.sembling carbon in some of its ]U’o}>erties ; all that at present need be st<at(‘d about it is that it forms with oxygen an oxide, ISitb, analogous in composition to th;it of carbon, ('(L This oxide, SiOj, is termed silica, or at times, silicic anhydride. I'dint and (|uart/. are almost chemically ])Ui-(‘ foians of silica; in this form silica is insoluble in w.atei- anrl all acids, and mixtures of acids, except hydro¬ fluoric acid. ()n being fused with an alkali, as KIB), or an .alkaline carbonate, silicai produces a glassy substance*, (‘iitirely solulile in watei-: this body is potassium silicate, K^SiO,, and from it, silicic acid.
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