PRESERVATIVES IN BUTTER. 311 



Solids not Pat.— The weight of salt found by titration is 

 subtracted from that of the residue left after the extraction of 

 the fat, and the difference represents the solids not fat. 



Fat. — The fat is best estimated by subtracting the total of the 

 water, salt, and solids not fat from 100 ; though the solvent may 

 be evaporated and the fat actually weighed, if desired. 



Curd. — An estimation of the actual curd present can be made 

 by submitting the residue, left after estimation of the fat, to 

 Kjeldahl's process for the estimation of nitrogen (p. 124), and 

 multiplying the nitrogen found by 6 '38. The milk-sugar may 

 be estimated in a portion of the solution used for the titration of 

 the salt by one of the methods given for the determination of 

 milk-sugar (p. 90). These determinations are rarely required. 



Casein is estimated by extracting the solids not fat with dilute 

 ammonia till no lumps are left, filtering the solution, and washing 

 the residue ; the filtrate is made acid with acetic acid, and the 

 precipitated casein collected 6n a tared filter or Gooch crucible, 

 and weighed as in the estimation of casein in milk (p. 129). The 

 extraction of the fat, and ignition may be, however, omitted, as 

 the fat has already been extracted, and the amount of ash is 

 so small that it may be neglected without great error. 



Ash. — In place of an estimation of the salt, an ash deter- 

 mination is often made, and the ash taken as salt. The results 

 are, however, always slightly above those obtained by titration, 

 as butter itself, to which no salt has been added, gives a small 

 ash ; preservatives, such as borax, will also swell the weight of 

 the ash. 



Preservatives. — The preservatives most largely used in 

 butter consist of sodium borates ; sulphites and nitrates have 

 also been used, usually in conjunction with borates ; fluorides 

 are also employed ; formalin has been recommended, but appears 

 to be rarely used. These should be tested for in the aqueous 

 portion which sinks to the bottom on melting the butter at a 

 low temperature. The reaction with turmeric paper applied 

 to the liquid direct will show the presence of free boric acid. 

 If no reaction or a feeble one be obtained, a little of the liquid 

 may be acidified with very dUute hydrochloric acid, and tested 

 with turmeric paper. A pinkish-brown coloration, turned 

 greenish-black by dilute alkali, will show the presence of boric 

 acid in combination. It wiU usually be found, if the butter 

 is preserved in this way, that a reaction is obtained from the 

 liquid itself, and a much stronger one after acidifying. The 

 presence of sulphites may almost always be detected by the 

 smell of sulphurous acid developed on acidifying. Nitrates may 

 be found by the diphenylamine test. Fluorides may be tested 

 for as in milk. For the quantitative estimation of preservatives 



