Formalin solution

To a few drops of formalin solution add a few drops of dinitro-phenylhydrazine reagent A (p. 263) a yellow precipitate is produced in the cold. Acetaldehyde and acetone give orange-coloured precipitates. Dissolve water-insoluble compounds e.g-y benzaldehyde, salicylalde-hyde, acetophenone and benzophenone) in a small volume of methanol before adding reagent B. With benzophenone the precipitate forms slowly. 

Sorensen s reaction. First read carefully the Estimation of Glycine, p. 463. Dissolve 0 2 g. of glycine in a few ml. of water in a test-tube A, add 2 drops of phenolphthalein and then very dilute NaOH solution drop by drop until the solution just turns pink. In a second test-tube B place 2 ml. of 40% formalin solution, add 2 drops of phenolphthalein solution and then the dil. NaOH solution until the solution just turns pink. Pour the contents of B into A and note the immediate decolorisation of the phenolphthalein, the solution now being acid. Observe also that several drops of dil. NaOH solution can now be added before the pink colour is restored. 

Place about 50 ml. of 40% formalin solution in a conical flask and add at least 10 drops of phenolphthalein solution. No add ery carefully from a burette dilute sodium hydroxide solution (il/ 10 will serve the purpose) until the solution is just faintly pink. 

The large value for the hemiformal formation constant of methanol and its low molecular weight explains the high efficiency of methanol in stabilizing formalin solutions. Phenol, on the other hand, is inefficient, and phenol hemiformals are only formed by careful removal of water (17). 

When rods are required they are placed in wooden trays in a formolising bath. If the requirement is for a disc or blank such as used by the button trade the extrudate is cut up by an automatic guillotine and the blanks are immersed in the formalin solution. For manufacture of sheets the rods are placed in moulds and pressed into sheets before formolising. Many attractive patterns may be made by pressing different coloured rods into grooves set on the bias to the rods, thus forming new multi-coloured rods. This operation may be repeated a number of times in order to produce complex patterns. 

Formaldehyde gas (Oxymethylene) HCHO 430 7.0-73.0 1.1 -21 Colourless Water soluble gas producing formalin solutions Suffocating odour Polymerizes readily Highly toxic Respiratory sensitizer... 

Formaldehyde has been rated as a possible carcinogen by the United States Occupational Safety and Health Act (OSHA) rules and should be handled with due caution. It is also a strong lacrymator and choking respiratory irritant. It irritates the skin, eyes, and mucous membranes [76]. Since it is used for tanning leather, it is obvious that fonnaldehyde has a high potential for reactions with proteins. Formaldehyde gas is flammable and most formalin solutions contain significant amounts of methanol, which is also volatile, toxic, and flammable. 

A mixture of 49 g of this ester compound, 76 g of 9B% formic acid and 6B ml of formalin solution is heated under reflux for B hours. The solvents are then removed in vacuo on the steam bath, the residue dissolved in water, made alkaline with ammonium hydroxide and extracted with chloroform. Removal of the solvent and distillation in vacuo yieids ethyl 4-di-methylaminocyclohexylcarboxylate, boiling point 122°C to 125°C/10 mm. 

Formaldehyde gas Fill one trough of a twin-trough chamber with 20 ml formalin solution (37%) [1, 2]. 

Dimethylol-o-cresol. A. Thirty seven percent formalin solution (16.2g) was added to a solution of o-cresol (lOg) and sodium hydroxide (4g) in 20 ml H20 at 0CC. After standing at room temperature for two days the solution was brought to pH 8.2 by the addition of 10% acetic acid and crystallization of 2,4-dimethylol-o-cresol began. 

The poor resolution of the fine structures of DNA and nucleosomes by conventional SEM was solved by the development of an ultrahigh-resolution SEM (14-15). Inaga et al. (16) observed the DNA double helix and nucleosomes of chicken erythrocytes by using an ultrahigh-resolution SEM. They modified the microspreading technique of Seki et al. (17) and combined it with the carbon plate method devised by Tanaka et al. (18). Briefly, they (procedures were performed at 0-4°C before fixation with the formalin solution) ... 

Formaldehyde solutions prepared by dissolving and depolymerization of paraformaldehyde (a homopolymer of formaldehyde with empirical formula HO (CH20)nH, where n > 6) are free of admixtures of methanol and formic acid. Depolymerized paraformaldehyde is useful in enzyme histochemistry, when the preservation of the enzyme activity is of crucial importance, but it has no advantage over formalin solutions routinely used in pathology and in immunohistochemistry. 

Technical Importance of the Aldehydes.—Formalin solution is used as a disinfectant and as a preservative. Caseinogen hardened with formaldehyde is a widely used substitute for vulcanite, as is also the synthetic resin bakelite, which is produced by the condensation of formaldehyde with phenol (p. 243). 

After the completion of the in vivo microdialysis experiment, rats are euthanized with an overdose of sodium pentobarbital (100 mg/kg) and perfused intracardially with 0.9% saline followed by 10% formalin. The brains are extracted and stored in a 10% formalin solution until they are sectioned into slices (40-60 mm) consecutively through the guide cannula tract. The sections are mounted onto gelatin-coated glass slides and stained with thionin. An observer unaware of the rat s treatment or results verifies the cannula location for each rat. 

Paraformaldehyde, (CH20)n where n is between 8 and 100, is a convenient polymer of formaldehyde. The polymer is easily formed by removing water from a 50% formalin solution under reduced pressure. As the formaldehyde concentration increases, crystals of paraformaldehyde form spontaneously. It is available at 91-97% purity. It is more stable than neat formaldehyde but just as useful in applications, where it readily decomposes back to the straight stuff. 

The industrial preparation of formaldehyde has occurred since the late 1800s and involves the catalytic oxidation of methanol 2CH,OH,. + 0 ,. —> 2CH 0,.. The oxidation takes place at temperatures between 400°C and 700°C in the presence of metal catalysts. Metals include silver, copper, molybdenum, platinum, and alloys of these metals. Formaldehyde is commonly used as an aqueous solution called formalin. Commercial formalin solutions vary between 37% and 50% formaldehyde. When formalin is prepared, it must be heated and a methanol must be added to prevent polymerization the final formalin solution contains between 5% and 15% alcohol. 

Preparation of Silver from Silver Chloride. Put 1 g of silver chloride and 1.8 ml of a 40% formalin solution into a porcelain beaker and add a 30% sodium hydroxide solution in small portions... 

Formalin test A small amount of formalin solution is injected into the hind paw of mice or rats. This induces a bi-phasic pain reaction and a specific pain-related behaviour. The first phase represents acute nociceptive pain, whereas the second phase indicates more persistent pain associated with inflammation and tissue damage. Pain behaviour is observed in both phases and measured by means of a scoring system. Besides opioids, compounds active against inflammatory and neuropathic pain can be detected (Dubuisson and Dennis, Pain 1977, 4, 161-174). 

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