Formalin

FORMALIN (formol), an aqueous solution of formaldehyde (CH₂O), usually containing methyl alcohol due to production conditions. Formaldehyde, HCHO, an aldehyde of formic acid, is a colorless gas with a suffocating odor, turning into a colorless liquid upon cooling to -21°C, solidifying at -92°C. The density relative to air is 1.04. Formaldehyde gives all the reactions of typical aldehydes. Upon oxidation, it turns into formic acid (HCHO + O -> HCOOH). Formalin is an energetic reducing agent, reducing (in an alkaline medium) oxides of heavy metals to simple bodies (HgO + HCHO -> Hg + HCOOH). It converts higher oxidation states of elements into lower ones. With ammonia, it gives a crystalline addition product: hexamethylenetetramine (see Urotropin) (6CH₂O + 4NH₃ -> 6H₂O + (CH₂)₆N₄). In general, formaldehyde possesses an extremely sharply expressed ability to give addition (condensation) products with the most diverse substances, in particular with amino acids and proteins. Formaldehyde is very prone to polymerization. Diverse polymerization products can be divided into a) the group of polyoxymethylenes—anhydrous polymerization products of the general formula (CH₂O)_n, little or not at all soluble in water, decomposing upon heating with the formation of formaldehyde; trioxymethylene (CH₂O)₃—a crystalline substance, soluble in water, chloroform, and alcohol; and b) the group of paraformaldehydes, polymers of the general formula (CH₂O)_n·mH₂O, spontaneously forming upon standing in strong formaldehyde solutions. Upon heating with water, it again gives soluble CH₂O. Formaldehyde is obtained by the oxidation of methyl alcohol in the form of vapors with atmospheric oxygen in the presence of catalysts (Pt, Cu, Ag), of which silver proved to be the most productive, but cheaper copper is used industrially. The resulting distillate is captured in water and gives formalin; the latter contains 35–40% formaldehyde, methyl alcohol (up to 15%), and about 50% water; sometimes with an admixture of acetone, formic and acetic acids, etc. The official preparation has a specific gravity of 1.081–1.086, usually a weakly acidic reaction, and must contain 37% CH₂O according to Pharmacopoeia VII. Upon evaporation of formalin, a dense mass of polymers insoluble in cold water remains. Formalin is recognized by its characteristic odor and the following reactions: 1) Formalin, when boiled with an equal volume of caustic alkali solution and a few crystals of resorcinol, gives an intensely red coloration; 2) with fuchsine-sulfurous acid—a raspberry coloration; 3) with aniline water (1%)—a white precipitate of methylene-phenylamine. When testing the quality of formalin, the main attention is paid to the absence of an excess of acids, and upon calcination—to the absence of a weighable residue, and especially to the proper percentage content of formaldehyde. Since two factors influence the specific gravity of the preparation—the percentage content of methyl alcohol and the percentage of formaldehyde—the determination of the percentage content by specific gravity alone is impossible. Quantitative determination is performed very accurately iodometrically: 5 cm³ of formalin (1:100) are mixed with 35 cm³ of Nessler's reagent containing 1% NaOH, 6% HgI₂, and 4% KI, and then 20 cm³ of caustic soda (15%). After standing for 15 minutes, it is acidified with 20 cm³ of 25% hydrochloric acid, and then 20 cm³ of 0.1 N iodine solution are added. The mercury dissolves; the excess iodine is back-titrated with 0.1 N thiosulfate solution (1 cm³ of 0.1 N iodine = 0.0015 g CH₂O) (Bougault, Gros). See also the determination of formaldehyde according to Pharmacopoeia VII (art. 225), as well as according to the All-Union Standard (OST No. 307). Formalin exhibits an energetic effect on the animal organism. Locally, it causes irreversible coagulation of protoplasm proteins, necrotizing or mummifying tissues. Taken internally, formalin causes sharp irritation of the mucous membranes. A 4% solution already causes necrosis of the mucous membranes. Blood hemoglobin is converted into methemoglobin. Taken internally, formalin causes pain and burning in the esophagus and stomach, then vomiting, often with blood-stained masses. Simultaneously, coughing, hyperemia of the ocular mucosa, sneezing, and dyspnea are observed. In parallel, phenomena from the central nervous system increase: dizziness, convulsions, unsteady gait, fear. Formalin is excreted partly with vomit, partially oxidized in the organism into formic acid, and in this form, along with unchanged formaldehyde, is excreted by the kidneys. The urinary tract is strongly irritated thereby; anuria and hemorrhagic nephritis are observed. Death occurs with phenomena of asphyxia and respiratory paralysis. A lethal outcome most often occurs within the first 24 hours, but fatal outcomes have been observed even several days after poisoning. The lethal dose is 10.0–15.0 of the official (~35%) solution. Upon autopsy: "the mucosa of the digestive tract is hyperemic and feels dry to the touch, with numerous ecchymoses. Formalin causes hemolysis: the blood is dark, usually filling the right atrium and ventricle; under the serous membranes, there are multiple ecchymoses. The abdominal organs are hyperemic. The liver is in a state of greater or lesser protein degeneration." Treatment of acute poisoning: weak ammonia solutions (0.1%), better a solution of ammonium acetate; milk, egg white with water; gastric lavage as early as possible. Chronic and occupational formaldehyde poisoning is observed in workers engaged in the manufacture of plastics (bakelite, galalith), in the chemico-pharmaceutical industry, in disinfectors during seed treatment, in pharmacy and chemical warehouses, and the paint and varnish industry. Symptoms: eye irritation, bronchitis, emaciation, headaches, hyperesthesia, sometimes corneal opacity, nail damage, dermatitis, disturbances of thermoregulation and sweating. Preventive measures: sealing of production processes and stocks of formalin, thorough ventilation of premises. Formalin possesses an energetic bactericidal action. Anthrax bacilli are killed within an hour by a 1:20,000 solution. Formalin vapors act especially energetically in the presence of water vapor. Formalin is widely used in medicine as a disinfectant (see Disinfectants) and medicinal agent. Its use as a preservative for food products is prohibited. In a very diluted form (0.25–0.5:1,000), formalin is used for washing wounds, gargling the throat; 0.5–1.0% solutions—for washing in cases of excessive sweating of the feet. Application on mucous membranes and wounds, however, is inconvenient due to the irritating properties of the preparation. In gynecology, solutions of 0.5–1.5 per 1 liter are prescribed for vaginal catarrh, endometritis. Usual prescription: Formalini 20.0, Aq. destill. 80.0. DS: one tablespoon (=20 cm³) per mug (1 liter). Formalin is not used internally. For the disinfection of internal organs, preparations that release formaldehyde in the organism are used (see Urotropin). When prescribing formalin, it should be kept in mind that the official preparation is taken as the unit, i.e., a 37% formaldehyde solution; therefore, a solution prepared, for example, according to the prescription Formalin 8%–100.0 contains only 3% formaldehyde. Paraformaldehyde, paraform—a mixture of solid polymers of formalin (see above), a white powder insoluble in water, alcohol, and ether, giving off the odor of formaldehyde upon heating. Soluble in ammonia and, upon heating, in dilute acids. Used for the disinfection of premises with the help of formalin lamps, in the form of tablets, often in a mixture with depolymerizing substances, such as CaO, BaO₂, KMnO₄. Methylal, dimethoxymethane [CH₂(OCH₃)₂], a colorless, easily mobile liquid with an ethereal odor, boiling at 42°, soluble in water (1:3), easily in alcohol and ether. Upon boiling with acids, it gives formaldehyde. Externally—as an analgesic agent. For inhalation anesthesia: 30–50.0. Naphthoformin, a condensation product of naphthol with formalin, a powder insoluble in water; dusting powder. Formamint, aromatized tablets with 0.01 paraformaldehyde and milk sugar. Proposed for the treatment of catarrhal conditions of the ear, throat, and nose. Moronal, basic formalin-sulfite of aluminum, a white powder, easily soluble in water. Aqueous solutions, under the action of acids, decompose into formaldehyde, sulfur dioxide, and aluminum hydroxide; used in a 1–2% solution as an antiseptic agent.

(S. Shubin). Formalin has found wide application in histological technique as a cheap and good fixing medium. For fixation, a 10-25% solution of it is used, which constitutes 4-10% formaldehyde. It should be kept in mind that in recipes for histological technique, strong commercial Formalin (representing a 40% solution of formaldehyde) is taken as 100%. It is better to use stronger solutions. Ordinary tap water, not distilled, is taken to avoid swelling of tissues; for fixation for the purpose of revealing finer structures, it is recommended to dilute Formalin in a physiological (0.85%) solution of table salt. Often, commercial Formalin has an acidic reaction, which in some cases can harm staining. For neutralization, a solution of caustic soda is added dropwise under the control of litmus paper or, even simpler, a layer of crushed chalk is poured onto the bottom of the bottle in which the Formalin is stored and shaken from time to time; as needed, the settled Formalin is poured off and diluted in the necessary way. When fixing in Formalin (as, indeed, in any fixative), it is necessary to ensure that it is not overloaded with the objects being fixed. It should be taken as a rule that for every 100 cm³ of formalin solution there should be no more than 3-5 pieces measuring 0.5 cm³ each. In general, pieces should not be taken very large; it is better if their thickness does not exceed 0.5-1 cm. However, in case of need, very large objects and even entire organs, e.g., the brain or heart, can be fixed in Formalin, from which the necessary pieces are cut out the next day, placing them in fresh Formalin. The criterion for the end of fixation is the browning of the blood pigment throughout the entire thickness of the piece taken, which is recognized upon cutting. For pieces 0.5-1 cm thick, 12-24 hours is a sufficient time. When fixing in a thermostat at a temperature of 37°, the fixation time can be halved. In pathological-anatomical practice, it is sometimes necessary to perform rapid fixation within a few (2-3) minutes, which is important for the urgent preparation of a finished specimen (response to a biopsy, histological diagnosis during an operation or autopsy). For this, the following procedure is followed: with a sharp knife, a thin slice is cut (preferably no thicker than 0.3-0.5 cm), placed in a test tube or small flask with a 20-25% Formalin solution and heated over a burner flame several times until boiling (but by no means boil). After 2-3 minutes, the fixation can be considered finished. After rinsing the pieces in water, they can be immediately decomposed into sections by the freezing method. The entire procedure for preparing the specimen in this way should take no more than 10-15 minutes. If material having the appearance of separate crumbs, scraps, or semi-liquid masses (mucus, tissue decay, vomit) is subject to fixation, then the indicated objects are fixed by first tying them tightly in gauze, and then embedding them in celloidin or paraffin. Smears made on glass slides (centrifuged exudates, discharge from mammary glands, punctates from tumors, etc.) are fixed in Formalin vapors, for which the slides are placed on a stand in a jar with a ground-glass stopper, at the bottom of which strong Formalin is poured. After such fixation (30-50 minutes), the smears, just like the sections, are passed through a staining battery and mounted in Canada balsam or gum syrup (if lipoids are stained). Besides all that has been said, formalin is an excellent medium for storing a histological archive. Material in it, after many fixatives (Zenker's fluid, Orth's fluid, etc.), can be stored for years, however, the most valuable pieces are still better stored in 80-96% alcohol. Formalin fixation has huge advantages over other methods of fixation. Material fixed in Formalin is suitable for preparing sections by any method, including the freezing method. The detection of lipoids and some methods of impregnation can be performed predominantly after fixation with Formalin. With all this, formalin fixation makes it possible to obtain fairly electively stained specimens with most of the staining methods used in pathological-histological practice. Among the disadvantages of formalin fixation, one can include the insufficient stainability of some protoplasmic granules and the fine structure of the nucleus, which makes it impossible to carry out some cytological techniques, and also the fact that formalin fixation often gives a precipitate in the form of small brown grains ("formalin pigment") in tissues rich in blood and during hemolysis, which to a certain extent spoils the specimen and can simulate vital deposits of some pigment. These precipitates can be removed either by transferring the sections for a few minutes into hydrogen peroxide (Devitsky's method), or by placing them for 10 minutes in a mixture of a 1% aqueous solution of caustic soda (1 part) with 80° alcohol (100 parts). After this, the sections are well washed in water and then in alcohol. In relation to sections prepared on a freezing microtome, one can limit oneself only to washing them for 5 minutes in a 2% solution of caustic soda with subsequent washing in water. In Formalin, one cannot fix tissues containing substances that are themselves soluble in it, such as, for example, glycogens, insignificant calcareous deposits, uric acid, etc. It should, however, be remembered that in acidic Formalin solutions, organs such as bones can also undergo decalcification (after several months). Formalin, besides its independent fixing significance, is often included as a component in various fixing mixtures (Orth's fluid, Regaud's fluid, Helly's fluid). See Fixation, Histological technique. For Formalin in museum technique, see Anatomical preparations.

(A. Kestner). Detection of formaldehyde in forensic chemical cases. Viscera are distilled with water vapor (see Poisons, isolation). The distillate is tested with the following reagents: 1) A portion of the distillate (1 cm³) is mixed with 5 cm³ of concentrated sulfuric acid. Upon wetting a grain of codeine with the resulting solution, a violet coloration appears immediately. 2) Concentrated hydrochloric acid (1-2 cm³ per 10 cm³ of distillate) and 1 cm³ of a solution of fuchsin-sulfurous acid are added to the distillate: a blue-violet or blue coloration appears. To prepare fuchsin-sulfurous acid, 0.1 g of fuchsin is dissolved in 100 cm³ of water, 5 cm³ of a saturated solution of acid sodium sulfite and 2 cm³ of concentrated hydrochloric acid are added. It must be kept in mind that heating can cause coloration of fuchsin-sulfurous acid without the presence of formaldehyde. 3) The distillate is mixed with an excess of ammonia and evaporated to dryness. The formation of hexamethylenetetramine (urotropine) occurs. The residue is dissolved in a few drops of water, and to individual drops, mercuric chloride (sublimate) and a solution of iodine in the presence of potassium iodide are added. Characteristic precipitates are obtained, which are compared under a microscope with preparations obtained from urotropine.