22 Mr. Phillips's Reply to Dr. Hope. [July, 



or of potash. When acetate of lead is decomposed by sulphate of 

 iron, two neutral compounds are produced ; and it is only from 

 the partial decomposition of the acetate of iron by heat that you 

 procure even the small product of acetic acid which you obtain. 

 Thus 10 ounces of acetate of lead contain very nearly 2*7 of 

 acetic acid, but by your process only 1*6 is obtained. 



In my remarks I stated that the quantities of the salts are not 

 such as are required for mutual decomposition; and I mentioned 

 it as probable that the quantity of sulphate of iron was too great 

 in the ratio of 18 to 7"5. By direct experiment, I find, however, 

 that the quantity is still more excessive than 1 had imagined. 

 Ten parts of acetate of lead require 2-1 of real sulphuric acid for 

 their decomposition ; but the 12 parts of dried sulphate of iron 

 which you employ contain 5*6 parts. 



But you tell me that it is " of advantage to employ this 

 excess. It facilitates," you say, " greatly the disengagement of 

 the acetic acid, and renders it unnecessary to raise the tempera- 

 ture to so high a pitch as would otherwise be required, by which 

 means the empyreuma, unavoidable in an elevated temperature, 

 is in a great measure prevented." 



First, as to the facility of the disengagement of the acetic 

 acid, and the low temperature at which it may be distilled. The 

 term low temperature is ot course comparative ; but having 

 frequently distilled stronger acetic acid than that obtained by 

 your process by means of a salt-water bath, I put into a retort ac- 

 cording to your formula six ounces of dried sulphate of iron and 

 five of acetate of lead. The temperature of the bath is about 

 224°; and the quantities of ingredients which I used are capable, 

 according to what I have just stated, of yielding one ounce and 

 three quarters of acetic acid. After having continued the heat 

 for five hours, I procured half the quantity of acid obtainable 

 from the acetate of lead :, it was, however, disagreeable and 

 empyreumatic. I repeated this experiment, continued the heat 

 for eight hours instead of five, and then obtained exactly 4-7ths of 

 the product yielded by the sand heat. From these statements, I 

 think but little must, be said in future about the facilities afforded 

 by the excess of sulphuric acid in disengaging the acetic. Even 

 when the temperature of a sand heat is employed, the operation 

 is excessively tedious, and extremely expensive, on account of 

 the quantity of fuel burned ; for in order to obtain the whole 

 product from five ounces of acetate of lead, amounting to only 

 I ounce 3-4ths of acetic acid, it required the application of eight 

 hours' fire. 



I shall now show that by employing the acetate of lead of 

 commerce, and a much smaller quantity of sulphuric acid than 

 you direct, a much greater proportion of a stronger acid may be 

 procured. 



Crystallized bisulphate of potash consists of 



