HOW TO PURIFY SALT FOR BUTTER. 565 



petre, however^ it is seldom used alone, but it is not uncommon to em- 

 ploy a mixture (;f common salt, saltpetre, and sugar, for the preservation 

 of butter. Where the butter has been washed, this admixture of cane- 

 sugar may supply the place of the milk-sugar which the butter originally 

 contained, and may impart to it a sweeter taste. 



The salt should be as pure as possible, as free, at least, from lime and 

 magnesia as it can be obtained, since these substances are apt to give 

 it a bitter or other disagreeable taste. It is easy, however, to purify the 

 common salt of the shops from these impurities by pouring a couple of 

 quarts of boiling water upon a stone or two of salt, stirring the whole 

 well about, now and then, for a couple of hours, and afterwards straining 

 it through a clean cloth. The water which runs through is a saturated 

 solution of salt, and contains all the impurities, but may be used for com- 

 mon culinary purposes or may be mixed with the food of the cattle. 

 The salt which remains on the cloth is free from the soluble salts of lime 

 and magnesia, and may be hung up in the cloth till it is dry enough to 

 be used for mixing with the butter or with cheese. 



The quantity of salt usually employed is from g^^th to 3-3 th part of the 

 weight of the butter — with which it ought to be well and thoroughly in- 

 corporated. The first sensible effect of the salt is to make the butter 

 shrink and diminish in bulk. It becomes more solid and squeezes out a 

 portion of the water — with which part of the salt also flows away. It is 

 not known that the casein actually combines with the salt, nor, if it did, 

 considering the very small (juantity of this substance which is present in 

 butter, could much salt be required for this purpose. But the points to 

 attend to in the salting of butter are to take care that all the water which 

 remains in the butter shall be fully saturated with salt — that is to say, 

 shall have dissolved as much as it can possibly take up — and that in no 

 part of the butter shall there be a particle of cheesy matter which is not 

 also in contact with salt. If you exclude the air, the presence of a sat- 

 urated solution of salt will not only preserve this cheesy matter from it- 

 self undergoing decay, but will i-ender it unable also to induce decay in 

 the sugar and fat which are in contact with it.* 



It is really extraordinary that such rigid precautions should be neces- 

 sary to prevent the evil influence of half a pound of cheesy matter, or less, 

 in a hundred pounds of butter (p. 551). 



5°. Though the curd or casein appears to be the enemy against whose 

 secret machinations the dairy farmer has chiefly to guard, yet tlie oxygen 

 of the atmosi)here is a second agent by which the fatty matters of butter 

 are liable to be brought into a state of decomposition, and the presence 

 of which, therefore, should be excluded as carefully as possible. 



We liave seen that by the action of oxygen the solid margaric acid of 

 butter may be changed into the oleic or liquid acid of butter (p. 560.) 



' Mr. Ballantyne thus describes the method of salting butter practised at his dairy farm of 

 30 cows, near Edinburgh :— " Ttie butter is drawn warm from tiie churn, and it is an invari- 

 able rule never to wash it or dip it into water, when intended to be salted. The dairymaid 

 puts it into a clean tub, which in previously well rinsed with cold water, and then works it 

 with cool hands till all the milk is thoroughly squeezed out. Half the allowed quantity of 

 salt is then added, and well mixed up with the butter, and in this state it is allowed to stand 

 till next morning, when it is asain wrou-fht up, any brine squeezed out, and the remainder 

 of the salt added. It is then packed into kits, which, when full, should be well covered up, 

 and placed in a cool dry store— a small quantity of salt is usually sprinkled on the surface. 

 The proportion of salt used at this dairy is half a-pound to fourteen pounds of butter. ■■'— 

 Journal of Agriculture, New Series, vol. I., p. 26. 

 24* 



