Chapter VII: Preface: To Volume Third (7)

(A) (B) (A) (B) (A) (B) (A) (B) (A) (B)
190 97.3 233 120.1 276 143.3 319 167.0 362 191.1
191 97.8 234 120.7 277 143.9 320 167.5 363 191.7
192 98.4 235 121.2 278 144.4 321 168.1 364 192.3
193 98.9 236 121.7 279 145.0 322 168.6 365 192.9
194 99.4 237 122.3 280 145.5 323 169.2 366 193.4
195 100.0 238 122.8 281 146.1 324 169.7 367 194.0
196 100.5 239 123.4 282 146.6 325 170.3 368 194.6
197 101.0 240 123.9 283 147.2 326 170.9 369 195.1
198 101.5 241 124.4 284 147.7 327 171.4 370 195.7
199 102.0 242 125.0 285 148.3 328 172.0 371 196.3
200 102.6 243 125.5 286 148.8 329 172.5 372 196.8
201 103.1 244 126.0 287 149.5 330 173.1 373 197.4
202 103.7 245 126.6 288 149.4 331 173.7 374 198.0
203 104.2 246 127.1 289 150.9 332 174.2 375 198.6
204 104.7 247 127.6 290 151.0 333 174.8 376 199.1
205 105.3 248 128.1 291 151.6 334 175.3 377 199.7
206 105.8 249 128.7 292 152.1 335 175.9 378 200.3
207 106.3 250 129.2 293 152.7 336 176.5 379 200.8
208 106.8 251 129.7 294 153.2 337 177.0 380 201.4
209 107.4 252 130.3 295 153.8 338 177.6 381 202.0
210 107.9 253 130.8 296 154.3 339 178.1 382 202.5
211 108.4 254 131.4 297 154.9 340 178.7 383 203.1
212 109.0 255 131.9 298 155.4 341 179.3 384 203.7
213 109.5 256 132.4 299 156.0 342 179.8 385 204.3
214 110.0 257 133.0 300 156.5 343 180.4 386 204.8
215 110.6 258 133.5 301 157.1 344 180.9 387 205.4
216 111.1 259 134.1 302 157.6 345 181.5 388 206.0
217 111.6 260 134.6 303 158.2 346 182.1 389 206.5
218 112.1 261 135.1 304 158.7 347 182.6 390 207.1
219 112.7 262 135.7 305 159.3 348 183.2 391 207.7
220 113.2 263 136.2 306 159.8 349 183.7 392 208.3
221 113.7 264 136.8 307 160.4 350 184.3 393 208.8
222 114.3 265 137.3 308 160.9 351 184.9 394 209.4
223 114.8 266 137.8 309 161.5 352 185.4 395 210.0
224 115.3 267 138.4 310 162.0 353 186.0 396 210.6
225 115.9 268 138.9 311 162.6 354 186.6 397 211.2
226 116.4 269 139.5 312 163.1 355 187.2 398 211.7
227 116.9 270 140.0 313 163.7 356 187.7 399 212.3
228 117.4 271 140.6 314 164.2 357 188.3 400 212.9
229 118.0 272 141.1 315 164.8 358 188.9 401 213.5
230 118.5 273 141.7 316 165.3 359 189.4 402 214.1
231 119.0 274 142.2 317 165.9 360 190.0 403 214.6
232 119.6 275 142.8 318 166.4 361 190.6 404 215.2

(A) (B) (A) (B) (A) (B) (A) (B) (A) (B)
405 215.8 417 222.8 429 229.8 441 236.9 453 244.0
406 216.4 418 223.3 430 230.4 442 237.5 454 244.6
407 217.0 419 223.9 431 231.0 443 238.1 455 245.2
408 217.5 420 224.5 432 231.6 444 238.7 456 245.7
409 218.1 421 225.1 433 232.2 445 239.3 457 246.3
410 218.7 422 225.7 434 232.8 446 239.8 458 246.9
411 219.3 423 226.3 435 233.4 447 240.4 459 247.5
412 219.9 424 226.9 436 233.9 448 241.0 460 248.1
413 220.4 425 227.5 437 234.5 449 241.6 461 248.7
414 221.0 426 228.0 438 235.1 450 242.2 462 249.3
415 221.6 427 228.6 439 235.7 451 242.8 463 249.9
416 222.2 428 229.2 440 236.3 452 243.4

=141. Meissl’s Table for Invert Sugar.=—Invert sugar is usually the product of the hydrolysis of sucrose. The following table is to be used when the hydrolysis is complete, _i_. _e_., when no sucrose is left in the solution. The solution of copper sulfate and of the alkaline tartrate are made up as follows: 34.64 grams of copper sulfate in half a liter, and 173 grams of rochelle salt and 51.6 grams sodium hydroxid in the same volume. The quantity of sugar solution used must not contain more than 245 nor less than ninety milligrams of invert sugar.

In the determination twenty-five cubic centimeters of the copper solution and an equal volume of the alkaline tartrate are mixed and boiled, the proper amount of sugar solution added to secure a quantity of invertose within the limits named, the volume completed to 100 cubic centimeters with boiling water, and the mixture kept in lively ebullition for two minutes. An equal volume of recently boiled cold water is added and the cuprous oxid at once separated by filtration on asbestos under pressure, and washed free of alkali with boiling water. The metallic copper is secured by one of the methods already described.

TABLE FOR INVERT SUGAR BY MEISSL AND WIEN.[107]

(A) = Milligrams of copper.
(B) = Milligrams of invert sugar.

(A) (B) (A) (B) (A) (B) (A) (B)
90 46.9 133 69.7 176 93.0 219 117.0
91 47.4 134 70.3 177 93.5 220 117.5
92 47.9 135 70.8 178 94.1 221 118.1
93 48.4 136 71.3 179 94.6 222 118.7
94 48.9 137 71.9 180 95.2 223 119.2
95 49.5 138 72.4 181 95.7 224 119.8
96 50.0 139 72.9 182 96.2 225 120.4
97 50.5 140 73.5 183 96.8 226 120.9
98 51.1 141 74.0 184 97.3 227 121.5
99 51.6 142 74.5 185 97.8 228 122.1
100 52.1 143 75.1 186 98.4 229 122.6
101 52.7 144 75.6 187 99.0 230 123.2
102 53.2 145 76.1 188 99.5 231 123.8
103 53.7 146 76.7 189 100.1 232 124.3
104 54.3 147 77.2 190 100.6 233 124.9
105 54.8 148 77.8 191 101.2 234 125.5
106 55.3 149 78.3 192 101.7 235 126.0
107 55.9 150 78.9 193 102.3 236 126.6
108 56.4 151 79.4 194 102.9 237 127.2
109 56.9 152 80.0 195 103.4 238 127.8
110 57.5 153 80.5 196 104.0 239 128.3
111 58.0 154 81.0 197 104.6 240 128.9
112 58.5 155 81.6 198 105.1 241 129.5
113 59.1 156 82.1 199 105.7 242 130.0
114 59.6 157 82.7 200 106.3 243 130.6
115 60.1 158 83.2 201 106.8 244 131.2
116 60.7 159 83.8 202 107.4 245 131.8
117 61.2 160 84.3 203 107.9 246 132.3
118 61.7 161 84.8 204 108.5 247 132.9
119 62.3 162 85.4 205 109.1 248 133.5
120 62.8 163 85.9 206 109.6 249 134.1
121 63.3 164 86.5 207 110.2 250 134.6
122 63.9 165 87.0 208 110.8 251 135.2
123 64.4 166 87.6 209 111.3 252 135.8
124 64.9 167 88.1 210 111.9 253 136.3
125 65.5 168 88.6 211 112.5 254 136.9
126 66.0 169 89.2 212 113.0 255 137.5
127 66.5 170 89.7 213 113.6 256 138.1
128 67.1 171 90.3 214 114.2 257 138.6
129 67.6 172 90.8 215 114.7 258 139.2
130 68.1 173 91.4 216 115.3 259 139.8
131 68.7 174 91.9 217 115.8 260 140.4
132 69.2 175 92.4 218 116.4 261 140.9

(A) (B) (A) (B) (A) (B) (A) (B)
262 141.5 305 166.8 348 192.6 391 219.3
263 142.1 306 167.3 349 193.2 392 219.9
264 142.7 307 167.9 350 193.8 393 220.5
265 143.2 308 168.5 351 194.4 394 221.2
266 143.8 309 169.1 352 195.0 395 221.8
267 144.4 310 169.7 353 195.6 396 222.4
268 144.9 311 170.3 354 196.2 397 223.1
269 145.5 312 170.9 355 196.8 398 223.7
270 146.1 313 171.5 356 197.4 399 224.3
271 146.7 314 172.1 357 198.0 400 224.9
272 147.2 315 172.7 358 198.6 401 225.7
273 147.8 316 173.3 359 199.2 402 226.4
274 148.4 317 173.9 360 199.8 403 227.1
275 149.0 318 174.5 361 200.4 404 227.8
276 149.5 319 175.1 362 201.1 405 228.6
277 150.1 320 175.6 363 201.7 406 229.3
278 150.7 321 176.2 364 202.3 407 230.0
279 151.3 322 176.8 365 203.0 408 230.7
280 151.9 323 177.4 366 203.6 409 231.4
281 152.5 324 178.0 367 204.2 410 232.1
282 153.1 325 178.6 368 204.8 411 232.8
283 153.7 326 179.2 369 205.5 412 233.5
284 154.3 327 178.8 370 206.1 413 234.3
285 154.9 328 180.4 371 206.7 414 235.0
286 155.5 329 181.0 372 207.3 415 235.7
287 156.1 330 181.6 373 208.0 416 236.4
288 156.7 331 182.2 374 208.6 417 237.1
289 157.2 332 182.8 375 209.2 418 237.8
290 157.8 333 183.5 376 209.9 419 238.5
291 158.4 334 184.1 377 210.5 420 239.2
292 159.0 335 184.7 378 211.1 421 239.9
293 159.6 336 185.4 379 211.7 422 240.6
294 160.2 337 186.0 380 212.4 423 241.3
295 160.8 338 186.6 381 213.0 424 242.0
296 161.4 339 187.2 382 213.6 425 242.7
297 162.0 340 187.8 383 214.3 426 243.4
298 162.6 341 188.4 384 214.9 427 244.1
299 163.2 342 189.0 385 215.5 428 244.9
300 163.8 343 189.6 386 216.1 429 245.6
301 164.4 344 190.2 387 216.8 430 246.3
302 165.0 345 190.8 388 217.4
303 165.6 346 191.4 389 218.0
304 166.2 347 192.0 390 218.7

=142. Table for the Determination of Invert Sugar (Reducing Sugars) in the Presence of Sucrose.=—The method adopted by the Association of Official Agricultural Chemists is essentially that proposed by Meissl and Hiller.[108] Prepare a solution of the material to be examined in such a manner that it contains twenty grams of the mixed sugars in one hundred cubic centimeters, after clarification and the removal of the excess of lead. Prepare a series of solutions in large test tubes by adding one, two, three, four, five etc. cubic centimeters of this solution to each tube successively. Add five cubic centimeters of the mixed copper reagent to each, heat to boiling, boil two minutes and filter. Note the volume of sugar solution which gives the filtrate lightest in tint, but still distinctly blue. Place twenty times this volume of the sugar solution in a 100 cubic centimeter flask, dilute to the mark, and mix well. Use fifty cubic centimeters of the solution for the determination, which is conducted as already described, until the weight of copper is obtained. For the calculation of the results use the following formulas and table of factors of Meissl and Hiller:[109]

Let Cu = the weight of the copper obtained;
P = the polarization of the sample;
W = the weight of the sample in the fifty cubic
centimeters of the solution used for determination;
F = the factor obtained from the table for conversion
of copper to invert sugar;
Cu
---- = approximate absolute weight of invert sugar = Z;
2

100
Z × ----- = approximate per cent of invert sugar = _y_;
W

100P
------- = R, relative number for sucrose;
P + _y_

100 - R = I, relative number for invert sugar;

Cu
---- = per cent of invert sugar.
W

Z indicates the vertical column, and the ratio of R to I, the horizontal column of the table, which are to be used for the purpose of finding the factor (F) for calculating copper to invert sugar.

_Example_:—The polarization of a sugar is 86.4, and 3.256 grams of it (W) are equivalent to 0.290 gram of copper. Then:

Cu 0.290
---- = ----- = 0.145 = Z
2 2

100 100
Z × ----- = 0.145 × ------ = 4.45 = _y_
W 3.256

100P 8640
-------- = ------------ = 95.1 = R
P + _y_ 86.4 + 4.45

100 - R = 100 - 95.1 = 4.9 = I

R : I = 95.1 : 4.9

By consulting the table it will be seen that the vertical column headed I = 150 is nearest to Z, 145, the horizontal column headed 95: 5 is nearest to the ratio of R to I, 95.1: 4.9. Where these columns meet we find the factor 51.2, which enters into the final calculation:

CuF .290 × 51.2
----- = ------------- = 4.56 the true per cent of invert sugar.
W 3.256

MEISSL AND HILLER’S FACTORS FOR THE DETERMINATION OF
MORE THAN ONE PER CENT OF INVERT SUGAR.

Ratio of Approximate absolute weight of invert sugar = _Z_.
sucrose I = I = I = I = I = I = I =
to invert 200 175 150 125 100 75 50
sugar = mg. mg. mg. mg. mg. mg. mg.
R : I.
0 : 100 56.4 55.4 54.5 53.8 53.2 53.0 53.0
10 : 90 56.3 55.3 54.4 53.8 53.2 52.9 52.9
20 : 80 56.2 55.2 54.3 53.7 53.2 52.7 52.7
30 : 70 56.1 55.1 54.2 53.7 53.2 52.6 52.6
40 : 60 55.9 55.0 54.1 53.6 53.1 52.5 52.4
50 : 50 55.7 54.9 54.0 53.5 53.1 52.3 52.2
60 : 40 55.6 54.7 53.8 53.2 52.8 52.1 51.9
70 : 30 55.5 54.5 53.5 52.9 52.5 51.9 51.6
80 : 20 55.4 54.3 53.3 52.7 52.2 51.7 51.3
90 : 10 54.6 53.6 53.1 52.6 52.1 51.6 51.2
91 : 9 54.1 53.6 52.6 52.1 51.6 51.2 50.7
92 : 8 53.6 53.1 52.1 51.6 51.2 50.7 50.3
93 : 7 53.6 53.1 52.1 51.2 50.7 50.3 49.8
94 : 6 53.1 52.6 51.6 50.7 50.3 49.8 48.9
95 : 5 52.6 52.1 51.2 50.3 49.4 48.9 48.5
96 : 4 52.1 51.2 50.7 49.8 48.9 47.7 46.9
97 : 3 50.7 50.3 49.8 48.9 47.7 46.2 45.1
98 : 2 49.9 48.9 48.5 47.3 45.8 43.3 40.0
99 : 1 47.7 47.3 46.5 45.1 43.3 41.2 38.1

=143. Table for the Estimation of Milk Sugar.=—The solutions to be used for this table are the same as those employed in the preceding table for the estimation of invert sugar. The milk sugar is supposed to be in a pure form in solution before beginning the analysis. The method to be employed for milk will be given in the part devoted to dairy products.

In the conduct of the work twenty-five cubic centimeters of the copper solution are mixed with an equal quantity of the alkaline tartrate mixture, and from twenty to one hundred cubic centimeters of the sugar solution added, according to its concentration. This solution should not contain less than seventy nor more than 306 milligrams of lactose. The volume is completed to 150 cubic centimeters with boiling water and kept in lively ebullition for six minutes. The rest of the operation is conducted in the manner already described. From the weight of copper obtained the quantity of milk sugar is determined by inspecting the table. It is recommended to use such a weight of milk sugar as will give about 200 milligrams of copper.

TABLE FOR DETERMINING MILK SUGAR.

(A) = Milligrams of copper.
(B) = Milligrams of milk sugar.

(A) (B) (A) (B) (A) (B) (A) (B)
100 71.6 120 86.4 140 101.3 160 116.4
101 72.4 121 87.2 141 102.0 161 117.1
102 73.1 122 87.9 142 102.8 162 117.9
103 73.8 123 88.7 143 103.5 163 118.6
104 74.6 124 89.4 144 104.3 164 119.4
105 75.3 125 90.1 145 105.1 165 120.2
106 76.1 126 90.9 146 105.8 166 120.9
107 76.8 127 91.6 147 106.6 167 121.7
108 77.6 128 92.4 148 107.3 168 122.4
109 78.3 129 93.1 149 108.1 169 123.2
110 79.0 130 93.8 150 108.8 170 123.9
111 79.8 131 94.6 151 109.6 171 124.7
112 80.5 132 95.3 152 110.3 172 125.5
113 81.3 133 96.1 153 111.1 173 126.2
114 82.0 134 96.9 154 111.9 174 127.0
115 82.7 135 97.6 155 112.6 175 127.8
116 83.5 136 98.3 156 113.4 176 128.5
117 84.2 137 99.1 157 114.1 177 129.3
118 85.0 138 99.8 158 114.9 178 130.1
119 85.7 139 100.5 159 115.6 179 130.8

(A) (B) (A) (B) (A) (B) (A) (B)
180 131.6 223 164.2 266 197.2 309 231.4
181 132.4 224 164.9 267 198.0 310 232.2
182 133.1 225 165.7 268 198.8 311 232.9
183 133.9 226 166.4 269 199.5 312 233.7
184 134.7 227 167.2 270 200.3 313 234.5
185 135.4 228 167.9 271 201.1 314 235.3
186 136.2 229 168.6 272 201.9 315 236.1
187 137.0 230 169.4 273 202.7 316 236.8
188 137.7 231 170.1 274 203.5 317 237.6
189 138.5 232 170.9 275 204.3 318 238.4
190 139.3 233 171.6 276 205.1 319 239.2
191 140.0 234 172.4 277 205.9 320 240.0
192 140.8 235 173.1 278 206.7 321 240.7
193 141.6 236 173.9 279 207.5 322 241.5
194 142.3 237 174.6 280 208.3 323 242.3
195 143.1 238 175.4 281 209.1 324 243.1
196 143.9 239 176.2 282 209.9 325 243.9
197 144.6 240 176.9 283 210.7 326 244.6
198 145.4 241 177.7 284 211.5 327 245.4
199 146.2 242 178.5 285 212.3 328 246.2
200 146.9 243 179.3 286 213.1 329 247.0
201 147.7 244 180.1 287 213.9 330 247.7
202 148.5 245 180.8 288 214.7 331 248.5
203 149.2 246 181.6 289 215.5 332 249.2
204 150.0 247 182.4 290 216.3 333 250.0
205 150.7 248 183.2 291 217.1 334 250.8
206 151.5 249 184.0 292 217.9 335 251.6
207 152.2 250 184.8 293 218.7 336 252.5
208 153.0 251 185.5 294 219.5 337 253.3
209 153.7 252 186.3 295 220.3 338 254.1
210 154.5 253 187.1 296 221.1 339 254.9
211 155.2 254 187.9 297 221.9 340 255.7
212 156.0 255 188.7 298 222.7 341 256.5
213 156.7 256 189.4 299 223.5 342 257.4
214 157.5 257 190.2 300 224.4 343 258.2
215 158.2 258 191.0 301 225.2 344 259.0
216 159.0 259 191.8 302 225.9 345 259.8
217 159.7 260 192.5 303 226.7 346 260.6
218 160.4 261 193.3 304 227.5 347 261.4
219 161.2 262 194.1 305 228.3 348 262.3
220 161.9 263 194.9 306 229.1 349 263.1
221 162.7 264 195.7 307 229.8 350 263.9
222 163.4 265 196.4 308 230.6 351 264.7

(A) (B) (A) (B) (A) (B) (A) (B)
352 265.5 365 276.2 377 286.5 389 296.8
353 266.3 366 277.1 378 287.4 390 297.7
354 267.2 367 277.9 379 288.2 391 298.5
355 268.0 368 278.8 380 289.1 392 299.4
356 268.8 369 279.6 381 289.9 393 300.3
357 269.6 370 280.5 382 290.8 394 301.1
358 270.4 371 281.4 383 291.7 395 302.0
359 271.2 372 282.2 384 292.5 396 302.8
360 272.1 373 283.1 385 293.4 397 303.7
361 272.9 374 283.9 386 294.2 398 304.6
362 273.7 375 284.8 387 295.1 399 305.4
363 274.5 376 285.7 388 296.0 400 306.3
364 275.3

=144. Table for the Determination of Maltose.=—The copper and alkaline solutions employed for the oxidation of maltose are the same as those used for invert and milk sugars.

In the manipulation twenty-five cubic centimeters each of the copper and alkali solutions are mixed and boiled and an equal volume of the maltose solution added, which should not contain more than one per cent of the sugar. The boiling is continued for four minutes, an equal volume of cold recently boiled water added, the cuprous oxid separated by filtration and the metallic copper obtained in the manner already described. The weight of maltose oxidized is then ascertained from the table.

_Example._ Weight of impure maltose taken, ten grams to a liter:
Quantity used, twenty-five cubic centimeters:
Weight of copper obtained 268 milligrams:
Weight of maltose oxidized 237 milligrams:
Weight of impure maltose taken 250 milligrams:
Percentage of maltose in sample 94.8.

TABLE FOR MALTOSE.

(A) = Milligrams of copper.
(B) = Milligrams of maltose.

(A) (B) (A) (B) (A) (B) (A) (B)
30 25.3 35 29.6 40 33.9 45 38.3
31 26.1 36 30.5 41 34.8 46 39.1
32 27.0 37 31.3 42 35.7 47 40.0
33 27.9 38 32.2 43 36.5 48 40.9
34 28.7 39 33.1 44 37.4 49 41.8

(A) (B) (A) (B) (A) (B) (A) (B)
50 42.6 94 81.2 138 120.6 182 160.1
51 43.5 95 82.1 139 121.5 183 160.9
52 44.4 96 83.0 140 122.4 184 161.8
53 45.2 97 83.9 141 123.3 185 162.7
54 46.1 98 84.8 142 124.2 186 163.6
55 47.0 99 85.7 143 125.1 187 164.5
56 47.8 100 86.6 144 126.0 188 165.4
57 48.7 101 87.5 145 126.9 189 166.3
58 49.6 102 88.4 146 127.8 190 167.2
59 50.4 103 89.2 147 128.7 191 168.1
60 51.3 104 90.1 148 129.6 192 169.0
61 52.2 105 91.0 149 130.5 193 169.8
62 53.1 106 91.9 150 131.4 194 170.7
63 53.9 107 92.8 151 132.3 195 171.6
64 54.8 108 93.7 152 133.2 196 172.5
65 55.7 109 94.6 153 134.1 197 173.4
66 56.6 110 95.5 154 135.0 198 174.3
67 57.4 111 96.4 155 135.9 199 175.2
68 58.3 112 97.3 156 136.8 200 176.1
69 59.2 113 98.1 157 137.7 201 177.0
70 60.1 114 99.0 158 138.6 202 177.9
71 61.0 115 99.9 159 139.5 203 178.7
72 61.8 116 100.8 160 140.4 204 179.6
73 62.7 117 101.7 161 141.3 205 180.5
74 63.6 118 102.6 162 142.2 206 181.4
75 64.5 119 103.5 163 143.1 207 182.3
76 65.4 120 104.4 164 144.0 208 183.2
77 66.2 121 105.3 165 144.9 209 184.1
78 67.1 122 106.2 166 145.8 210 185.0
79 68.0 123 107.1 167 146.7 211 185.9
80 68.9 124 108.0 168 147.6 212 186.8
81 69.7 125 108.9 169 148.5 213 187.7
82 70.6 126 109.8 170 149.4 214 188.6
83 71.5 127 110.7 171 150.3 215 189.5
84 72.4 128 111.6 172 151.2 216 190.4
85 73.2 129 112.5 173 152.0 217 191.2
86 74.1 130 113.4 174 152.9 218 192.1
87 75.0 131 114.3 175 153.8 219 193.0
88 75.9 132 115.2 176 154.7 220 193.9
89 76.8 133 116.1 177 155.6 221 194.8
90 77.7 134 117.0 178 156.5 222 195.7
91 78.6 135 117.9 179 157.4 223 196.6
92 79.5 136 118.8 180 158.3 224 197.5
93 80.3 137 119.7 181 159.2 225 198.4

(A) (B) (A) (B) (A) (B) (A) (B)
226 199.3 245 216.3 264 233.4 283 250.4
227 200.2 246 217.2 265 234.3 284 251.3
228 201.1 247 218.1 266 235.2 285 252.2
229 202.0 248 219.0 267 236.1 286 253.1
230 202.9 249 219.9 268 237.0 287 254.0
231 203.8 250 220.8 269 237.9 288 254.9
232 204.7 251 221.7 270 238.8 289 255.8
233 205.6 252 222.6 271 239.7 290 256.6
234 206.5 253 223.5 272 240.6 291 257.5
235 207.4 254 224.4 273 241.5 292 258.4
236 208.3 255 225.3 274 242.4 293 259.3
237 209.1 256 226.2 275 243.3 294 260.2
238 210.0 257 227.1 276 244.2 295 261.1
239 210.9 258 228.0 277 245.1 296 262.0
240 211.8 259 228.9 278 246.0 297 262.8
241 212.7 260 229.8 279 246.9 298 263.7
242 213.6 261 230.7 280 247.8 299 264.6
243 214.5 262 231.6 281 248.7 300 265.5
244 215.4 263 232.5 282 249.6

=145. Preparation of Levulose.=—It is not often that levulose, unmixed with other reducing sugars, is brought to the attention of the analyst. It probably does not exist in the unmixed state in any agricultural product. The easiest method of preparing it is by the hydrolysis of inulin. A nearly pure levulose has also lately been placed on the market under the name of diabetin. It is prepared from invert sugar.

Inulin is prepared from dahlia bulbs by boiling the pulp with water and a trace of calcium carbonate. The extract is concentrated to a sirup and subjected to a freezing temperature to promote the crystallization of the inulin. The separated product is subjected to the above operations several times until it is pure and colorless. It is then washed with alcohol and ether and is reduced to a fine powder. Before the repeated treatment with water it is advisable to clarify the solution with lead subacetate. The lead is afterwards removed by hydrogen sulfid and the resultant acetic acid neutralized with calcium carbonate.

By the action of hot dilute acids inulin is rapidly converted into levulose.

Levulose may also be prepared from invert sugar, but in this case it is difficult to free it from traces of dextrose. The most successful method consists in forming a lime compound with the invert sugar and separating the lime levulosate and dextrosate by their difference in solubility. The levulose salt is much less soluble than the corresponding compound of dextrose. In the manufacture of levulose from beet molasses, the latter is dissolved in six times its weight of water and inverted with a quantity of hydrochloric acid, proportioned to the quantity of ash present in the sample. After inversion the mixture is cooled to zero and the levulose precipitated by adding fine-ground lime. The dextrose and coloring matters in these conditions are not thrown down. The precipitated lime levulosate is separated by filtration and washed with ice-cold water. The lime salt is afterwards beaten to a cream with water and decomposed by carbon dioxid. The levulose, after filtration, is concentrated to the crystallizing point.[110]

=146. Estimation of Levulose.=—Levulose, when free of any admixture with other reducing sugars, may be determined by the copper method with the use of the subjoined table, prepared by Lehmann.[111] The copper solution is the same as that used for invert sugar, _viz._, 69.278 grams of pure copper sulfate in one liter. The alkali solution is prepared by dissolving 346 grams of rochelle salt and 250 grams of sodium hydroxid in water and completing the volume to one liter.

_Manipulation._—Twenty-five cubic centimeters of each solution are mixed with fifty of water and boiled. To the boiling mixture twenty-five cubic centimeters of the levulose solution are added, which must not contain more than one per cent of the sugar. The boiling is then continued for fifteen minutes, and the cuprous oxid collected, washed and reduced to the metallic state in the usual way. The quantity of levulose is then determined by inspection from the table given below. Other methods of determining levulose in mixtures will be given further on.

TABLE FOR THE ESTIMATION OF LEVULOSE.

(A) = Milligrams of copper.
(B) = Milligrams of levulose.

(A) (B) (A) (B) (A) (B) (A) (B)
20 7.15 62 31.66 104 56.85 146 82.81
21 7.78 63 32.25 105 57.46 147 83.43
22 8.41 64 32.84 106 58.07 148 84.06
23 9.04 65 33.43 107 58.68 149 84.68
24 9.67 66 34.02 108 59.30 150 85.31
25 10.30 67 34.62 109 59.91 151 85.93
26 10.81 68 35.21 110 60.52 152 86.55
27 11.33 69 35.81 111 61.13 153 87.16
28 11.84 70 36.40 112 61.74 154 87.88
29 12.36 71 37.00 113 62.36 155 88.40
30 12.87 72 37.59 114 62.97 156 89.05
31 13.46 73 38.19 115 63.58 157 89.69
32 14.05 74 38.78 116 64.21 158 90.34
33 14.64 75 39.38 117 64.84 159 90.98
34 15.23 76 39.98 118 65.46 160 91.63
35 15.82 77 40.58 119 66.09 161 92.26
36 16.40 78 41.17 120 66.72 162 92.90
37 16.99 79 41.77 121 67.32 163 93.53
38 17.57 80 42.37 122 67.92 164 94.17
39 18.16 81 42.97 123 68.53 165 94.80
40 18.74 82 43.57 124 69.13 166 95.44
41 19.32 83 44.16 125 69.73 167 96.08
42 19.91 84 44.76 126 70.35 168 96.77
43 20.49 85 45.36 127 70.96 169 97.33
44 21.08 86 45.96 128 71.58 170 97.99
45 21.66 87 46.57 129 72.19 171 98.63
46 22.25 88 47.17 130 72.81 172 99.27
47 22.83 89 47.78 131 73.43 173 99.90
48 23.42 90 48.38 132 74.05 174 100.54
49 24.00 91 48.98 133 74.67 175 101.18
50 24.59 92 49.58 134 75.29 176 101.82
51 25.18 93 50.18 135 75.91 177 102.46
52 25.76 94 50.78 136 76.53 178 103.11
53 26.35 95 51.38 137 77.15 179 103.75
54 26.93 96 51.98 138 77.77 180 104.39
55 27.52 97 52.58 139 78.39 181 105.04
56 28.11 98 53.19 140 79.01 182 105.68
57 28.70 99 53.79 141 79.64 183 106.33
58 29.30 100 54.39 142 80.28 184 106.97
59 29.89 101 55.00 143 80.91 185 107.62
60 30.48 102 55.62 144 81.55 186 108.27
61 31.07 103 56.23 145 82.18 187 108.92

(A) (B) (A) (B) (A) (B) (A) (B)
188 109.56 232 138.57 276 168.68 320 199.97
189 110.21 233 139.25 277 169.37 321 200.71
190 110.86 234 139.18 278 170.06 322 201.44
191 111.50 235 140.59 279 170.75 323 202.18
192 112.14 236 141.27 280 171.44 324 202.91
193 112.78 237 141.94 281 172.14 325 203.65
194 113.42 238 142.62 282 172.85 326 204.39
195 114.06 239 143.29 283 173.55 327 205.13
196 114.72 240 143.97 284 174.26 328 205.88
197 115.38 241 144.65 285 174.96 329 206.62
198 116.04 242 145.32 286 175.67 330 207.36
199 116.70 243 146.00 287 176.39 331 208.10
200 117.36 244 146.67 288 177.10 332 208.83
201 118.02 245 147.35 289 177.82 333 209.57
202 118.68 246 148.03 290 178.53 334 210.30
203 119.33 247 148.71 291 179.24 335 211.04
204 119.99 248 149.40 292 179.95 336 211.78
205 120.65 249 150.08 293 180.65 337 212.52
206 121.30 250 150.76 294 181.63 338 213.25
207 121.96 251 151.44 295 182.07 339 213.99
208 122.61 252 152.12 296 182.78 340 214.73
209 123.27 253 152.81 297 183.49 341 215.48
210 123.92 254 153.49 298 184.21 342 216.23
211 124.58 255 154.17 299 184.92 343 216.97
212 125.24 256 154.91 300 185.63 344 217.72
213 125.90 257 155.65 301 186.35 345 218.47
214 126.56 258 156.40 302 187.06 346 219.21
215 127.22 259 157.14 303 187.78 347 219.97
216 127.85 260 157.88 304 188.49 348 220.71
217 128.48 261 158.49 305 189.21 349 221.46
218 129.10 262 159.09 306 189.93 350 222.21
219 129.73 263 159.70 307 190.65 351 222.96
220 130.36 264 160.30 308 191.37 352 223.72
221 131.07 265 160.91 309 192.09 353 224.47
222 131.77 266 161.63 310 192.81 354 225.23
223 132.48 267 162.35 311 193.53 355 225.98
224 133.18 268 163.07 312 194.25 356 226.74
225 133.89 269 163.79 313 194.97 357 227.49
226 134.56 270 164.51 314 195.69 358 228.25
227 135.23 271 165.21 315 196.41 359 229.00
228 135.89 272 165.90 316 197.12 360 229.76
229 136.89 273 166.60 317 197.83 361 230.52
230 137.23 274 167.29 318 198.55 362 231.28
231 137.90 275 167.99 319 199.26 363 232.05

(A) (B) (A) (B) (A) (B) (A) (B)
364 232.81 370 237.39 376 241.87 382 246.25
365 233.57 371 238.16 377 242.51 383 247.17
366 234.33 372 238.93 378 243.15 384 248.08
367 235.10 373 239.69 379 243.79 385 248.99
368 235.86 374 240.46 380 244.43
369 236.63 375 241.23 381 245.34

=147. Precipitation of Sugars with Phenylhydrazin=.—The combination of phenylhydrazin with aldehyds and ketones was first studied by Fischer, and the near relationship of these bodies to sugar soon led to the investigation of the compounds formed thereby with this reagent.[112] Reducing sugars form with phenylhydrazin insoluble crystalline bodies, to which the name osazones has been given. The reaction which takes place is a double one and is represented by the following formulas:

Dextrose. Phenylhydrazin. Dextrose-phenylhydrazone.

C₆H₁₂O₆ + C₆H₅NH.NH₂ = C₆H₁₂O₅.N.NHC₆H₅ + H₂O
and C₆H₁₂O₅.N.NHC₆H₅ + C₆H₅NH.NH₂ =
Phenyldextrosazone.
C₆H₁₀O₄(N.NHC₆H₅)₂ + 2H₂O.

The dextrosazone is commonly called glucosazone. The osazones formed with the commonly occurring reducing sugars are crystalline, stable, insoluble bodies which can be easily separated from any attending impurities and identified by their melting points. Glucosazone melts at 205°, lactosazone at 200° and maltosazone at 206°.

The osazones are precipitated in the following way: The reducing sugar, in about ten per cent solution, is treated with an excess of the acetate of phenylhydrazin in acetic acid and warmed to from 75° to 85°. In a short time the separation is complete and the yellow precipitate formed is washed, dried and weighed. The sugar can be recovered from the osazone by decomposing it with strong hydrochloric acid by means of which the phenylhydrazin is displaced and a body, osone, is formed, which by treatment with zinc dust and acetic acid, is reduced to the original sugar. The reactions which take place are represented by the following equations:[113]

Glucososone.
C₆H₁₀O₄(N.NH.C₆H₅)₂ + 2H₂O = C₆H₁₀O₆ + 2C₆H₅N₂H₂

Dextrose (Glucose).
C₆H₁₀O₆ + H₂ = C₆H₁₂O₆.

For the complete precipitation of dextrose as osazone Lintner and Kröber show that the solution of dextrose should not contain more than one gram in 100 cubic centimeters. Twenty cubic centimeters containing 0.2 gram dextrose should be used for the precipitation.[114] To this solution should be added one gram of phenylhydrazin and one gram of fifty per cent acetic acid. The solution is then to be warmed for about two hours and the precipitate washed with from sixty to eighty cubic centimeters of hot water and dried for three hours at 105°. One part of the osazone is equivalent to one part of dextrose when maltose and dextrin are absent. When these are present the proportion is one part of osazone to 1.04 of dextrose. Where levulose is precipitated instead of dextrose 1.43 parts of the osazone are equal to one part of the sugar.

Sucrose is scarcely at all precipitated as osazone until inverted.

After inversion and precipitation as above, 1.33 parts osazone are equal to one part of sucrose.

The reaction with phenylhydrazin has not been much used for quantitive estimations of sugars, but it has been found especially useful in identifying and separating reducing sugars. It is altogether probable, however, that in the near future phenylhydrazin will become a common reagent for sugar work.

Maquenne has studied the action of phenylhydrazin on sugars and considers that this reaction offers the only known means of precipitating these bodies from solutions where they are found mixed with other substances.[115] The osazones, which are thus obtained, are usually very slightly soluble in the ordinary reagents, for which reason it is easy to obtain them pure when there is at the disposition of the analyst a sufficient quantity of the material. But if the sugar to be studied is rare and if it contain, moreover, several distinct reducing bodies, the task is more delicate. It is easy then to confound several osazones which have almost identical points of fusion; for example, glucosazone with galactosazone. Finally, it becomes impossible by the employment of phenylhydrazin to distinguish glucose, dextrose or mannose from levulose alone or mixed with its isomers. Indeed, these three sugars give, with the acetate of phenylhydrazin the same phenylglucosazone which melts at about 205°. It is noticed that the weights of osazones which are precipitated when different sugars are heated for the same time with the same quantity of the phenylhydrazin, vary within extremely wide limits. It is constant for each kind of sugar if the conditions under which the precipitation is made are rigorously the same. There is then, in the weight of the osazones produced, a new characteristic of particular value. The following numbers have been obtained by heating for one hour at 100°, one gram of sugar with 100 cubic centimeters of water and five cubic centimeters of a solution containing forty grams of phenylhydrazin and forty grams of acetic acid per hundred. After cooling the liquid, the osazones are received upon a weighed filter, washed with 100 cubic centimeters of water, dried at 110° and weighed. The weights of osazones obtained are given in the following table:

Weight of the osazones.
Character of the sugar. gram.

Sorbine, crystallized 0.82
Levulose ” 0.70
Xylose ” 0.40
Glucose, anhydrous 0.32
Arabinose, crystallized 0.27
Galactose ” 0.23
Rhamnose ” 0.15
Lactose ” 0.11
Maltose ” 0.11

With solutions twice as dilute as those above, the relative conditions are still more sensible, and the different sugars arrange themselves in the same order, with the exception of levulose, which shows a slight advantage over sorbine and acquires the first rank. From the above determinations, it is shown that levulose and sorbine give vastly greater quantities of osazones, under given conditions, than the other reducing sugars. It would be easy, therefore, to distinguish them by this reaction and to recognize their presence also even in very complex mixtures, where the polarimetric examination alone would furnish only uncertain indications.

It is remarkable that these two sugars are the only ones among the isomers or the homologues of dextrose, actually known, which possess the functions of an acetone. They are not, however, easily confounded, since the glucosazone forms beautiful needles which are ordinarily visible to the naked eye, while the sorbinosazone is still oily and when heated never gives perfectly distinct crystals.

This method also enables us to distinguish between dextrose and galactose, of which the osazone is well crystallized and melts at almost the same temperature as the phenylglucosazone. Finally, it is observed that the reducing sugars give less of osazones than the sugars which are not capable of hydrolysis, and consequently differ in their inversion products. It is specially noticed in this study of the polyglucoses (bioses, trioses), that this new method of employing the phenylhydrazin appears very advantageous. It is sufficient to compare the weights of the osazones to that which is given under the same conditions by a known glucose, in order to have a very certain verification of the probabilities of the result of the chemical or optical examination of the mixture which is under study. All the polyglucoses which have been examined from this point of view give very decided results. The numbers which follow have reference to one gram of sugar completely inverted by dilute sulfuric acid, dissolved in 100 cubic centimeters of water, and treated with two grams of phenylhydrazin, the same quantity of acetic acid, and five grams of crystallized sodium acetate. All these solutions have been compared with the artificial mixtures and corresponding glucoses, with the same quantities of the same reagents. The following are the results of the examination:

Weight of the osazone.
Character of the sugar. gram.

1 {Saccharose, ordinary 0.71
{Glucose and levulose (.526 g each) 0.73

2 {Maltose 0.55
{Glucose (1.052 g) 0.58

3 {Raffinose, crystallized 0.48
{Levulose, glucose and galactose (.333 g each) 0.53

4 {Lactose, crystallized 0.38
{Glucose and galactose (.500 g each) 0.39

It is noticed that the agreement for each saccharose is as satisfactory as possible. Numbers obtained with the products of inversion are always a little low by reason of the destructive action of sulfuric acid, and in particular, upon levulose. This is, moreover, quite sensible when the product has to be heated for a long time with sulfuric acid in order to secure a complete inversion. It is evident from the data cited from the papers of Fischer, Maquenne, and others, that the determination of sugars by this method is not a very difficult analytical process and may, in the near future, become of great practical importance.

=148. Molecular Weights of Carbohydrates.=—In the examination of carbohydrates the determination of the molecular weights is often of the highest analytical value.

The uncertainty in respect of the true molecular weights of the carbohydrates is gradually disappearing by reason of the insight into the composition of these bodies, which recently discovered physical relations have permitted.

Raoult, many years ago,[116] proposed a method of determining molecular weights which is particularly applicable to carbohydrates soluble in water.

The principle of Raoult’s discovery may be stated as follows: The depression of the freezing point of a liquid, caused by the presence of a dissolved liquid or solid, is proportionate to the absolute amount of substance dissolved and inversely proportionate to its molecular weight.

The following formulas may be used in computing results:

_C_ = observed depression of freezing point:

_P_ = weight of anhydrous substance in 100 grams:

_C_
--- = _A_ = depression produced by one gram substance in 100 grams:
_P_

_K_ = depression produced by dissolving in 100 cubic centimeters a number of grams of the substance corresponding to its molecular weight:

_M_ = molecular weight:

_C_
Then we have, _K_ = ---- × _M_.
_P_

_K_ is a quantity varying with the nature of the solvent but with the same solvent remaining sensibly constant for numerous groups of compounds.

The value of

_C_
_A_ ----
_P_

can be determined by experiment. The molecular weight can therefore be calculated from the formula

_K_
_M_ = ----.
_A_

With organic compounds in water the value of _K_ is almost constant.

Brown and Morris[117] report results of their work in extending Raoult’s investigations of the molecular weight of the carbohydrates. The process is carried on as follows:

A solution of the carbohydrate is prepared containing a known weight of the substance in 100 cubic centimeters of water. About 120 cubic centimeters of the solution are introduced into a thin beaker of about 400 capacity. This beaker is closed with a stopper with three holes. Through one of these a glass rod for stirring the solution is inserted. The second perforation carries a delicate thermometer graduated to 0°.05. The temperature is read with a telescope. The beaker is placed in a mixture of ice and brine at a temperature from 2° to 3° below the freezing point of the solution. The solution is cooled until its temperature is from 0°.5 to 1° below the point of congelation. Through the third aperture in the stopper a small lump of ice taken from a frozen portion of the same solution, is dropped, causing at once the freezing process to begin. The liquid is briskly stirred and as the congelation goes on the temperature rises and finally becomes constant. The reading is then taken. The depression in the freezing point, controlled by the strength of the solution, should never be more than from 1° to 2°.

The molecular weights may also be determined by the boiling points of their solutions as indicated by the author,[118] Beckmann,[119] Hite, Orndorff and Cameron.[120]

The method applied to some of the more important carbohydrates gave the following results:

DEXTROSE.

Calculated for C₆H₁₂O₆. Found.
_M_ = 180 _M_ = 180.2

SUCROSE.

Calculated for C₁₂H₂₂O₁₁. Found.
_M_ = 342 _M_ = 337.5

INVERTOSE (DEXTROSE AND LEVULOSE).

Calculated for C₆H₁₂O₆. Found.
_M_ = 180 _M_ = 174.3

MALTOSE.

Calculated for C₁₂H₂₂O₁₁. Found.
_M_ = 342 _M_ = 322

LACTOSE.

Calculated for C₁₂H₂₂O₁₁. Found.
_M_ = 342 _M_ = 345

ARABINOSE.

Calculated for C₅H₁₀O₅. Found.
_M_ = 150 _M_ = 150.3

RAFFINOSE.
Calculated for
C₁₈H₃₂O₁₆.5H₂O. Found.
_M_ = 594 _M_ = 528

=149. Birotation.=—As is well known, dextrose exhibits in fresh solutions the phenomenon of birotation. The authors supposed that this phenomenon might have some relation to the size of the molecule. They, therefore, determined the molecular volume of freshly dissolved dextrose by the method of Raoult and found _M_ = 180. The high rotatory power of recently dissolved dextrose is therefore not due to any variation in the size of its molecule.

The mathematical theory of birotation is given by Müller as follows.[121] In proportion as the unstable modification _A_ is transformed into the stable modification _B_, the rotation will vary. Let ρ = the specific rotatory power of _B_ and _a_ρ = that of _A_, both in the anhydrous state. Let now _p_ grams of the substance be dissolved in _V_ cubic centimeters of solvent and observed in a tube _l_ decimeters in length. The time from making the solution is represented by θ. The angle of rotation α is read at the time θ. Let _x_ = the mass of _A_, and _y_ = that of _B_, and the equation is derived.

_a_ρ_xl_ ρ_yl_
α = --------- + ------:
_V_ _V_

But _x_ + _y_ = _p_

ρ_l_
whence α = [(_a_ - 1)_x_ + _p_] ----.
_V_

If now there be introduced into the calculation the final angle of rotation αₙ, which can be determined with great exactness; we have

_p_ρ_l_ (_a_ - 1)_x_
αₙ = ------- and consequently α = αₙ[1 + ------------],
_V_ _p_

(_a_ - 1)_x_ α
whence ------------- = --- - 1.
_p_ αₙ

This equation gives the quantity _x_ of the unstable matter which is transformed into the stable modification in the time θ.

It must be admitted that the quantity _dx_ which is changed during the infinitely small time _d_θ is proportional to the mass _x_ which still exists at the moment θ, whence _dx_ = -Cʹ_xd_θ where Cʹ represents a constant positive factor. From this is derived the equation

_dx_
----- = -Cʹ_d_θ.
_x_

Integrating and calling _x_ the quantity of matter changed to the stable form at the moment θ, corresponding to a rotation α₀, we have

1 _x_₀
Cʹ = ------- log. nap. ----, and taking into consideration
θ - θ₀ _x_

the equation given above, and substituting common for superior logarithms we get

1 α₀ - αₙ
C = --------- log. ---------.
θ - θ₀ α - αₙ

Experience has shown that such a constant C really exists, and its value can be easily calculated from the data of Parcus and Tollens.[122] The mean value of C from these data is 0.0301 for arabinose; 0.0201 for xylose; 0.0393 for rhamnose; 0.0202 for fucose; 0.00927 for galactose; 0.00405 for lactose; 0.00524 for maltose, and for dextrose, 0.00348 at 11° to 13° and 0.00398 from 13° to 15°. The constant C as is well known, increases as the temperature is raised.

The constant C, at a given temperature, measures the progress of the phenomenon of the change from the unstable to the stable state. It will be noticed that among the sugars possessing multirotation properties the pentoses possess a much higher speed of transformation than the others.

=150. Estimation of Pentose Sugars and Pentosans as Furfurol.=—The production of furfurol by distilling carbohydrates with an acid has already been mentioned. Tollens and his associates have shown that with pentose sugars, and carbohydrate bodies yielding them, the production of furfurol is quantitive.

The production and estimation of furfurol have been systematically studied by Krug, to whose paper the reader is referred for the complete literature of the subject.[123] The essential principles of the operation are based on the conversion of the pentoses into furfurol by distilling with a strong acid, and the subsequent precipitation and estimation of the furfurol formed in the first part of the reaction.

The best method of conducting the distillation is as follows:

Five grams of the pentose substance are placed in a flask of about a quarter liter capacity, with 100 cubic centimeters of hydrochloric acid of 1.06 specific gravity. The arrangement of the apparatus is shown in Fig. 46. The flame of the lamp is so regulated as to secure about two cubic centimeters of distillate per minute.

The distillate is received in a graduated cylinder and as soon as thirty cubic centimeters are collected, an equal quantity of hydrochloric acid, of the strength noted, is added to the distilling flask, allowing it to flow in slowly so as not to stop the ebullition. The process is continued until a drop of the distillate gives no sensible reaction for furfurol when tested with anilin acetate. The test is applied as follows: Place a drop of the distillate on a piece of filter paper moistened with anilin acetate. The presence of furfurol will be disclosed by the production of a brilliant red color. Usually about three hours are consumed in the distillation, during which time a little less than 400 cubic centimeters of distillate is obtained. The distillate is neutralized with solid sodium carbonate and, in order to have always the same quantity of common salt present, 10.2 grams of sodium chlorid are added for each fifty cubic centimeters of water necessary to make the total volume to half a liter.[124]

The reactions with pentosans probably consist in first splitting up of the molecule into a pentose and the subsequent conversion of the latter into furfurol according to the following equations:

(C₅H₈O₄)ₙ + (H₂O)ₙ = (C₅H₁₀O₅)ₙ
Pentosan. Water. Pentose.

and

(C₅H₁₀O₅)ₙ = (C₅H₄O₂)ₙ + (3H₂O)ₙ.
Pentose. Furfurol. Water.

=151. Determination of Furfurol.=—The quantity of furfurol obtained by the process mentioned above may be determined in several ways.

_As Furfuramid._—When ammonia is added to a saturated solution of furfurol, furfuramid, (C₅H₄O)₃N₂, is formed. In order to secure the precipitate it is necessary that the furfurol be highly concentrated and this can only be accomplished by a tedious fractional distillation. This method, therefore, has little practical value.

_As Furfurolhydrazone._—Furfurol is precipitated almost quantitively, even from dilute solutions, by phenylhydrazin. The reaction is represented by the equation:

C₆H₈N₂ + C₅H₄O₂ = C₁₁H₁₀N₂O + H₂O.
Phenylhydrazin. Furfurol. Furfurolhydrazone. Water.

=152. Volumetric Methods.=—Tollens and Günther have proposed a volumetric method which is carried out as follows:[125] The distillation is accomplished in the manner described. The distillate is placed in a large beaker, neutralized with sodium carbonate and acidified with a few drops of acetic. Phenylhydrazin solution of known strength is run in until a drop of the liquid, after thorough mixing, shows no reaction for furfurol with anilin acetate. The reagent is prepared by dissolving five grams of pure phenylhydrazin and three of glacial acetic acid in distilled water, and diluting to 100 cubic centimeters. The solution is set by dissolving from two-tenths to three-tenths gram of pure furfurol in half a liter of water and titrating with the phenylhydrazin as indicated above. The quantity of the pentose used has a great influence on the result.

With nearly a gram of arabinose about fifty per cent of furfurol were obtained while when nearly five grams were used only about forty-six per cent of furfurol were found. With xylose a similar variation was found, the percentage of furfurol, decreasing as the quantity of pentose increased. The method, therefore, gives only approximately accurate results.

=153. Method of Stone.=—Another volumetric method proposed by Stone is based on the detection of an excess of phenylhydrazin by its reducing action on the fehling reagent.[126] A standard solution of phenylhydrazin is prepared by dissolving one gram of the hydrochlorate and three grams of sodium acetate in water and completing the volume of the liquor to 100 cubic centimeters. This solution contains 1.494 milligrams of phenylhydrazin in each cubic centimeter, theoretically equivalent to 1.328 milligrams of furfurol. The reagent is set by titrating against a known weight of furfurol. Pure furfurol may be prepared by treating the crude article with sulfuric acid and potassium dichromate, and subjecting the product to fractional distillation. The distillate is treated with ammonia and the furfuramid formed is purified by recrystallizing from alcohol and drying over sulfuric acid. One gram of this furfuramid is dissolved in dilute acetic acid and the volume completed to one liter with water.[127] The phenylhydrazin solution being unstable, is to be prepared at the time of use.

The titration is conducted as follows: Twenty-five cubic centimeters of the distillate obtained from a pentose body, by the method described above, are diluted with an equal volume of water, a certain quantity of the phenylhydrazin solution added to the mixture from a burette and the whole heated quickly to boiling. The flask is rapidly cooled and a portion of its contents poured on a filter. The filtrate should have a pale yellow color and be perfectly clear. If it become turbid on standing, it should be refiltered. Two cubic centimeters of the clear filtrate are boiled with double the quantity of the fehling reagent. If phenylhydrazin be present, the color of the mixture will change from blue to green. By repeating the work, with varying quantities of phenylhydrazin, a point will soon be reached showing the end of the reaction in a manner entirely analogous to that observed in volumetric sugar analysis.

In practice the volumetric methods have given place to the more exact gravimetric methods described below.

=154. Gravimetric Methods.=—The distillation is carried on and the volume of the distillate completed to half a liter as described above. Chalmot and Tollens then proceed as follows:[128] Ten cubic centimeters of a solution of phenylhydrazin acetate, containing in 100 cubic centimeters twelve grams of the phenylhydrazin and seven and a half grams of glacial acetic acid dissolved and filtered, are added to the distillate and the mixture stirred with an appropriate mechanism for half an hour. The furfurolhydrazone at the end of this time will have separated as small reddish-brown crystals. The mixture is then thrown onto an asbestos filter and the liquid separated with suction. The suction should be very gradually applied so as not to clog the felt. The precipitate adhering to the beaker is washed into the filter with 100 cubic centimeters of water. The precipitate is dried at about 60° and weighed. As a check the hydrazone may be dissolved in hot alcohol, the filter well washed, dried and again weighed. To obtain the weight of furfurol the weight of hydrazone found is multiplied by 0.516 and 0.025 added to compensate for the amount which was held in solution or removed by washing. Less than one per cent of pentose can not be determined by this method since that amount is equalled by the known losses during the manipulation.

_Factor._—To convert the furfurol found into pentoses, the following factors are used:

Per cent furfurol Multiply for
obtained from Multiply for Multiply for penta-glucoses
five grams of arabinose by. xylose by. by.
pentoses.

2.5 per cent or less 1.90 1.70 1.67
5.0 ” ” ” more 2.04 1.90 1.92

=155. Method Of Krug.=—In conducting the determination of furfurol, according to the method of Chalmont and Tollens just noticed, Krug observed that the filtrate, after standing for some time, yielded a second precipitate of furfurol hydrazone. Great difficulty was also experienced in collecting the precipitate upon the filter on account of the persistency with which it stuck to the sides of the vessel in which the precipitation took place.[129] In order to avoid these two objections, Krug modified the method as described below and this modified method is now exclusively used in this laboratory.