May 



?•] 



SCIENCE. 



425 



manufacture. The presence of this sulphate of lime must be re- 

 garded as objectionable. None of these powders are as strong as 

 they might be made, and most of them are very deficient in 

 strength. Apart from questions of healthfulness, there can be no 

 economy in buying some of these powders. 



IV. Ahim-Pmvders. — Here are classed the powders showing 

 the same re-actions as the preceding class, but free from phos- 

 phates. All appeared to be ammonia alum-powders, but re-actions 

 for potash and tartaric acid were not wanting among them. Only 

 one of them begins to come up to the strength which a " straight" 

 burnt ammonia alum-powder might have. 



V. Unclassed Powders. — The composition of these is such as 

 to present their coming under any of the previous heads. 



/. Cream-of -Tartar Powders. 



III. Alum and Phosphate Powders. 



//. Acid-Phosphate-of-Lime Powders. 



IV. Alum Powders. 



Note.— Since the rapidity with which a baking-powder gives off carbonic-acid 

 gas in the cold varies with the ingredients used, it was deemed worth while to test 

 some powders as follows ; Forty-five grains (three grams) of each was mixed, with as 

 little shaking as possible, with one-sixth ounce (five cubic centimetres) of water, and 

 the volume of gas evolved in five minutes was measured. 





