SUGAR.— Loaf. 911

1 lb. of steam of the tension given, or 24,000 X35‘2 = 844,800 lbs. = 84,480 gallons required forthis one pan of sugar.

For all technical calculations it will suffice toassume that each pound of vapour from the pancontains 1150 units of heat; and then knowing thetemperature of the condensing water before andafter use, to determine the quantity of it requiredby the method illustrated above. It must notbe forgotten in estimating for the size of pumps,pipes, &c., to supply the water, that the consump-tion will be much larger in the first part of theboiling than in the last.

Steam Required. —Assuming that there is no lossof heat by radiation, leakage, &c., and that thevapour from the pan is saturated steam of a tem-perature corresponding to its tension (this lastassumption introduces but a slight error), the heatto be communicated by the “ boiler steam ” in theworms and jacket will be, first, that required toraise the original 54,000 lbs. of liquor (assuming,which is not quite correct, that it has the samespecific heat as water) from, say, 100° Fahr. to 130°Fahr., or about 1,620,000 units; and then to con-vert 24,000 lbs. of -water of this temperature intosteam, containing 1145 units of heat* per lb. (seesupra) : (24,000 X 1145) — (24,000 X 130) =24,360,000 units of heat, or 25,980,000 units ofheat must be given to the sugar liquor by the steamin the worms and jacket. If the steam used has atension of 30 lbs. above atmospheric pressure, andthe water condensed from it runs away through thecondense box at a temperature corresponding tothis pressure, or 274° Fahr., then as steam of thispressure contains 1197 units per lb., and the waterresulting from its condensation at this pressure con-tains 276 units, each pound of steam affords 921units of heat effective for evaporating the water in25,980,000

the pan — -- — 28,208-5 of steam are

required, without allowing anything for waste inany way—as by condensing in the pipes, radiationfrom the pans, &c. If we compare with this thequantity of heat required to evaporate the samequantity of water at atmospheric pressure, as in anopen pan, we shall see how small is the savingin the amount of heat effected by the use of thevacuum pan.

Assume the mean temperature of the boilingliquor to be 220° Fahr., then

Units of Heat.

54,000 Ills, raised from 160° Fahr. tol , . ,.

220“ Fahr.j- = 6,480,000

24,000 lbs. water at 220° Fahr. con-)

verted into steam of the same tem- = about 23,040,000

perature, at 960 units per pound,... )

29,520,000

which is only 14 per cent, more than that requiredby the first.

Boiling to Grain. —The liquor is drawn into the pan,at first high enough to cover the bottom worm and* Reckoned from 0’ Fahr.

the jacket, if there be one. Steam is turned on, andthe liquor boiled down rapidly till it begins to growsomewhat viscid, as shown by a drop or two re-moved from the pan by the “proof-stick” drawingout to a thread between the finger and thumb. Thehigher the proof (i.e., the longer the thread) the“ charge ” is carried to, the larger will be the numberof grains of sugar made when granulation does takeplace, and consequently the smaller will be the ulti-mate size of the grains after boiling the pan full—■other things being the same. When the workmanjudges the proof (and this will vary with the degree ofpurity of the liquor he is using) to be right for theparticular kind of grain he wishes to make, he letsthe temperature of the mass rise somewhat, runs ina fresh portion of unboiled liquor, which disturbsthe state of supersaturation in which the boiledliquor was, and induces the formation of more orless of sugar crystals. These first appear as littlebright specks (“sparks”) floating in the “proof,”and afterwards rapidly increase in size. They arefed by the constant admission of fresh unthickenedliquor till they attain the size wished, or till the panis full. In the first case the admission of liquor isstopped, and the concentration continued to a degreeof “stoutness” as great as is compatible with thesubsequent working of the mass, which is then letentirely out of the pan. If the grain (crystal) hasnot attained the required size when the pan isfull, a portion—say one-half or two-thirds—of thecontents are let out, and then boiling resumed. Thecomparatively few crystals left in the pan nowreceive on their surfaces nearly all the sugar de-posited from the fresh portions of liquor as they areevaporated, and consequently grow fast. Thisletting out (“ cutting”) is sometimes repeated sevenor eight times, so that the final panful of very bigcrystals has been as much as twenty-four hoursboiling.

The actual working of a pan, as applied to theboiling of various qualities of raw sugar and ofsyrups of varying degrees of exhaustion, can onlybe taught or learnt at the pan itself.

"ViTether ] ar g e crystals or small have been made,their mother liquor must be separated from them.The most obvious and most simple way of doingthis is to put the mass into a vessel in which it candrain. This is done in loaf-sugar making.

Loaf Sugar. — The granular magma of sugarcrystals and syrup, which is a hot saturated solutionof sugar plus the impurities of the raw, as it leavesthe pan is received in heaters or jacketed pans, pro-vided or not with mechanical stirrers, and broughtto a temperature of about 180° to 190° Fahr. Itis next filled out into a number of conical moulds,each holding from 7 to 12 lbs. of it, and allowedto stand for from twelve to twenty hours to cool.During this time the sugar held in solution in thesyrup by virtue of the high temperature crystallizesout, and cements the existing grains of sugar firmlytogether.

The stopper which closed the hole in the apex of| each mould is then removed, and a steel pricker is