Impurities originating from the cream of tartar employed are estimated as previously described; and the amount of starch contained is determined by the usual methods. In some preparations, tartaric acid is substituted for cream of tartar. The following proportions represent the composition of a baking powder of good quality:-- Parts. Cream of tartar 30 Sodium bicarbonate 15 Flour 5 (_b_) _Sodium bicarbonate and calcium diphosphate._--Calcium sulphate occurs as an impurity in the commercial phosphate and is therefore liable to be met with in phosphate powders. In addition to phosphoric acid, lime, etc., a determination of sulphuric acid and chlorine should be made. (_c_) _Sodium bicarbonate and alum._--These constitute the most reprehensible forms of baking powder. The sanitary effects of alum have been referred to under Flour. It may be present either as potash or ammonia alum. The following is a fair example of an alum powder:-- Per cent. Alum 26·45 Sodium bicarbonate 24·17 Ammonium sesquicarbonate 2·31 Cream of tartar None Starch 47·07 From an exhaustive investigation of baking powders made by Dr. Henry A. Mott, it was found that about 50 per cent. of these preparations were impure, alum being the chief admixture. Of 280 samples of cream of tartar lately examined by various American Health Boards, 100 were adulterated; of 95 baking powders tested, 16 were adulterated. SUGAR. The sugars of commerce may be conveniently classified into two varieties, viz., sucrose (cane sugar or saccharose) and dextrose (grape sugar or glucose). The former, which is the kind almost exclusively employed for domestic uses, is chiefly obtained from the sugar cane of the West Indies and American Southern States (_Saccharum officinarum_), and, in continental Europe, from the sugar beet (_Beta vulgaris_). A comparatively small quantity is manufactured in the United States from the sugar maple (_Acer saccharinum_), and from sorghum (_Sorghum saccharatus_).